Assuming no proton decay, its life span (for baryonic beings such as us) is far beyond 10^1500 years, so I don't think that "lifespan of the universe" is a limiting factor here. Nobody's speaking of living an infinitely long life.

Indefinite doesn’t mean infinite.

When is the universe definitely going to die?

If the if is certain the when doesn’t matter.

How certain could anyone possibly be on this subject? I can agree it likely doesn't matter to us either way.