Regarding generators for hospitals and other critical facilities, placing these at high level rather than in a basement is clearly more sensible in case of flooding, but is by no means a cure all.
My work involves the servicing and testing of generators, and assisting in enquiries after they have failed to function.

IME, generators in large buildings seldom work as intended/as expected. The most common problems seem to be be

Defective or discharged starter batteries.
Lack of ventilation resulting in overheating.
Generator starts but soon stops or breaks due to overloading.
Engine starts but no power supplied to building due to defective, mis-applied, or mis-understood changeover switchgear.
Runs out of fuel, the tank being sized for only a few hours operation, and then not even kept full.
Runs out of lubricating oil, no one having realised that that this needs topping up on a long run.
Or finaly, it all works fine, but someone in charge sends everyone home because they feel that for example powering only 25% of the lighting is unsafe.

My experiences are in the UK, but I suspect that circumstances are broadly similar elswhere.