I think those are going to be run until they die. The capex vs opex is too high to obsolete them in a few years. They'll keep serving current gen LLMs for as long as they keep running.

I think you are right when you factor in the much more efficient newer high end GPU. That is what may make the current GPu investments obsolete in 2-4 years.

aiui nvidia has buyback agreements covering these to prevent them from being sold off

H100 were released in Oct 2022. They are now more expensive than at release time.