I have not heard of too many cases that you can run a tube till it "ends"!
Yes! Tubes have a life span, but it does not usually mean they will stop working. They just deteriorate in sound quality (become less dynamic compared to a healthy tube!) very gradually.
Most of us have at least a few sets of tubes to roll, and from my (limited) experience with my audiophile friends, this never happens!
We will find a new favorite set before the tubes get to much used.