On paper, this all makes a lot of sense. What is going to happen when these airplanes start falling out of the sky because they are just too old?

50 years is a long time for a piece of machinery. There will be many failure modes that will be discovered in these planes.

The C-130 was thought to last forever. Until about 10 years ago, well used planes being used for firefighting starting having structural failure in flight. Suddenly, organizations flying the older airframes decided that it was no longer effective to take the risk of failure.