Are Las Vegas landmarks made to last?  

After all of the landmark original hotels
have been imploded, I doubt that there's much left of the vintage original Las Vegas.
Among the fatalities:
-Big Red's Casino: Closed in 1982.
-Boardwalk Hotel and Casino: Demolished May 9, 2006 to make way for CityCenter.
-Bourbon Street Hotel and Casino: Demolished February 6, 2006, now an empty lot.
-Desert Inn (and golf course): Inn demolished in 2004, now Wynn Las Vegas; golf course retained and improved.
-The Dunes (and golf course): Demolished in 1993, now Bellagio.
-El Rancho (formerly Thunderbird/Silverbird): Closed in 1992 and demolished in 2000,
-El Rancho Vegas: Burned down in 1960.
-Glass Pool Inn: Demolished in 2006. It was called Mirage Motel until 1988 and changed names due to The Mirage opening down The Strip in 1989.
-Hacienda: Demolished in 1996, now Mandalay Bay. A separate Hacienda now exists outside of Boulder City, formerly the Gold Strike Inn.
-Holy Cow Casino Cafe and Brewery First micro brewery in Las Vegas. Closed in 2002, property currently vacant.
-Jackpot Casino: Closed in 1977, now the Sahara.
-Klondike Hotel & Casino: Closed in 2006, demolished in 2008.
-The Landmark: Demolished in 1995. Now the site of a parking lot for the Las Vegas Convention Center (Demolition was filmed for the feature Mars Attacks!).
-Lucky Slots Casino: Closed in 1981, now a shopping center.
-Lotus Inn Hotel & Casino: Closed in 1978, now a Rodeway Inn.
-Money Tree Casino: Closed in 1979.
-Marina Hotel and Casino: Westward pointing tower (known as the West Wing) of the MGM Grand.
-The New Frontier: Closed July 16, 2007, demolished November 13, 2007. Was to have been replaced by the new Las Vegas Plaza, but that project was put on hold.
-Nob Hill Casino: Closed in 1990, now Casino Royale.
-Paddlewheel Hotel & Casino: Closed in 1991 and reopened in 1993 as Debbie Reynolds' Hollywood Hotel & Casino, which itself closed in 1996 and is now the Greek Isles Hotel & Casino.
-San Souci: Closed in 1962 for the Castaways, which itself was demolished in 1987. Now the site of The Mirage.
-The Sands: Demolished in 1996, now The Venetian.
-Silver City Hotel & Casino: Closed in 1999, now the Silver City Shopping Center.
-Silver Slipper: Demolished in 1988 for a parking lot. Now the site of the Desert Inn Road Arterial.
-Stardust Resort & Casino: Closed November 1, 2006, demolished March 13, 2007. Was to have been replaced by Echelon Place, but that project was put on hold in August 2008.
-Tally Ho Hotel: Closed in 1966. Became the Aladdin, which in 2007 became Planet Hollywood.
-Vacation Village Resort & Casino; Closed in 2002, demolished in 2006. Site of the new Town Square development.
-Vegas World: Demolished in 1995 and rebuilt as the Stratosphere; parts of the old Vegas World still remain.
-Westward Ho Hotel and Casino: Closed in 2005, demolished in 2006

This is a very interesting question...
To me, Vegas has five phases, so far.
Vegas 1.0--the 1950s when it was just transforming from a desert town with some whore houses into a crook's dream of a gambling/entertainment town.
Vegas 2.0--the 1960's to mid 1970's Vegas, when it was a fully realized version of a crook's dream of a gambling/entertainment town. During this phase, a maverick oligarch named Howard Hughes entered and paved the way for the conventional oligarchs to take over the action subsequently.
Vegas 3.0--mid 1970s to mid 1980s, when the oligarchy decided to follow Howard Hughes' lead and come in and give the hoods the boot and grab the action. The quid pro quo for organized crime going quietly was apparently turning a blind eye to organized crime moving and redeveloping its gaming/entertainment action onto Native American reservations all over America.
Vegas 4.0--mid 1980s to mid 1990s, when the oligarchic owners try to broaden the appeal of Vegas to most adults, rather than just gambling adults.
Vegas 5.0--mid 1990s to present, when the oligarchic owners decided to hybridize it into a combination of adult gaming/entertainment and "fun for the whole family." 🙂
The idea from Version 3.0 onward was apparently always to create a core gaming/entertainment industry that could be grown and then diversified and thus allow the city itself to be rebranded and re-marketed, so as to create that most prized real estate development opportunity of all--the mega growth city that one has control over the timing of the development of. Game, set, match. They did that, whether one likes it or not!

continued
With all that said, the answer to your question is complex. The casino/hotels themselves are monuments to their builders on the one hand. In this sense they are meant to last. On the other hand, they have to attract huge numbers of customers and architectural spectacle are crucial to doing that; i.e., being the latest have to see and experience place are organic to the Las Vegas business dynamic.
Put it this way, the casinos in Monaco, or Portugal, can be stately, because those places will attract many persons, regardless. But no one wants to come to Las Vegas, Nevada, unless their is a slam bang architectural and gaming/entertainment experience to be had.
So: it is organic to the Las Vegas context and business dynamic that most gaming/entertaimnent buildings, once they lose their thrill-capacity, and once their debt has been sufficiently retired to allow for land use succession,get torn down and replaced with something hopefully more spectacular.
There are, in the final analysis, two reasons why the tear down and rebuild dynamic is so strong there:
1) spectacle is needed to attract business;
2) the gaming/entertainment businesses that build and operate the buildings make massive amounts of money and have a drastically shorter cummulative payback on investment, so, in turn, it is financially feasible to tear down and rebuild much faster than on other more conventional buildings, like, say, office buildings;

continued
4) the more spectacular the facility, the less need there is to be "close" to the existing spectacles, so there is a tendancy to stretch out the strip, as well as rebuild on existing hotel sites. This supply elasticity of land keeps the land value gradient low enough that land owners can never really create a compelling land oligopoly to stimulate land value drastically upwards (as occurs, say, in places like London, NYC, San Francisco, Hong Kong) and so retard the temptation to tear down and rebuild with exhorbitant land costs; and
5)finally the demand for gaming/entertaiment really has continued to spike in an America that has in effect spent much of the last century on gaming prohibition, and so there really is demonstrable opportunity for scaling up the size of the gaming/entertainment developments.
Las Vegas is not only a good city for the likes of Robert Venturi to study for aesthetics of complexity and contradiction, but for all persons in all fields dealing in urbanization to study, because it is recent, and simple enough to grasp some of its dynamics and explain them to others.
The problem, of course, is that many foolish people fail to recognize some of the underlying uniqueness of dynamics at play there (some of which I have alluded to above), and so generalize too broadly, or worse, try to impose sensibilities and conventions from, say, cities like NYC, upon what is in essense a still youthful, overgrown, oligopoly company town attempting to diversify into some semblance of a city through traditional means of diversification.
Based on my own fond memories of Versions 2.0 and forward, it is a shame several of the great old hotel/casinos could not have been been saved...for architectural significance.
But the only way to have done that would have been to have legislated a monopoly for the old Mafia that protected the old Mafia from the predatory economic power of the oligarchic investors that took over much of the action in Vegas.
The present Las Vegas absolutely required the long dynamic of show topping architectural spectacle in order to evolve into what it is, for better, or worse.

Post Script about organized crime and Native American casinos...
I did not mean to leave an impression that organized crime has, for a fact, an involvement in Native American gaming/entertainment facilities. It is just reputed by some to be the case. For all I know, gaming/entertainment facilities on Native American reservations could be entirely uninfluenced by organized crime. The facts regarding the drivers of the rapid emergence of gaming/entertainment facilities on Native American reservations, will likely come out some considerable time in the future, as happened with the history of the Las Vegas gaming/entertainment industry, and as is often the case with many fast emerging industries. Again, I have seen no conclusive evidence one way, or the other, on this issue and certainly do not wish to leave an impression that I have seen such, or that any evidence of anything untoward now exists to my knowledge.

Post Post Script on Nobody Wanting to Come to Vegas without...
a slam bang gaming/entertainment experience. Here again, I have to revise my own remarks for the sake of accuracy. What I meant to say was relatively few vacationers from across USA and around the world would wish to come to Las Vegas, Nevada, without the kind of architectural spectacle and gaming/entertainment experience that Vegas offers.
Las Vegas itself has become a pretty decent American city in many respects, IMHO, over the last 15 years. I once considered living there for work-related reasons, but the heat was just too much for me.
So: Las Vegans, do not consider my remarks generally disparaging of your desert oasis. Vacationers often prefer not to spend their hard earned vacations in many fine cities lacking in a strong recreational/entertainment vector such as that found in Las Vegas.
Ah, the vissisitudes of internet commentary.