How long is an artificial island suppose to last?
The ones in the Chesapeake Bay Bridge Tunnel have been around since 1964.
It depends on a lot of things-- current, materials, engineering and placement. Japan has done a great job with artificial islands. Kansai International Airport is probably the model of artificial island engineering. It survived the 1995 Great Hanshin Earthquake with minimal damage. That being said, it wasn't cheap to build and is not cheap to maintain nor operate.
These projects can potentially make sense in a densely populated country like Japan, but only barely. They do not generally make sense in a desert kingdom such as the U.A.E. This helps explain why developers are more inclined to use glitter and gimmicks to promote the projects and less inclined to invest in top-notch engineering to make sure the artificial islands last.
FWIW, while Kansai International Airport may be the best known example of the Japanese expertise in building artificial islands, it is far from the only example. Port Island and Rokko Island are older and more commercially successful neighborhoods of Kobe which also successfully weathered the Great Hanshin Earthquake. That being said, neither were without problems during the big earthquake. Small sections of the islands needed reinforcement and additional landfill (due to a quicksand-like liquefaction in scattered places) after that earthquake. One can only imagine how a Dubai like development put together without the same type of engineering and construction expertise would have fared under similar circumstances.
At least until the checks clear the bank.