Apartment and bungalow lifespan

What happens to a flat / apartment at the end of building’s useful life (may be 50 years later)? Should the owners just vacate and go away and their investment in the flat becomes zero? Further, what is the average lifespan of an apartment building versus a bungalow in karachi and what is the preferable mode of living?

In most cases, your investment becomes zero after completion of life span of a flat/apartment. It also becomes zero in case of cracks in building. There is no ownership of issues in building. A house on land is far better for your future generations. The house can be demolished to build a new one by children or their children.