Alan is this a grafted tree or a seedling? The majority of comments I’ve heard about short lived pawpaws relate to grafts dying and the rootstock continuing onward with new root suckers. I’m not experienced enough to have first hand insight, but I’d imagine pruning back and encouraging new growth could actually prolong the life of a tree. Hard to say without trying it.
*I have had two grafted cultivars (Atwood and Susquehanna) die back to the rootstock this year, but they were only a few years old so it was something other than old age that got them. I’ll be grafting the rootstock sprouts to try again next year.