I don't think anyone in the 616 continuity knows that, tho. (And it's not clear if the 616 Changeling's power is anything like the Changeling/Morph in the Exiles, since they demonstrated very different powersets, personalities and appearances.)
In any event, using husks from folks with potent regenerative abilities like Wolverine or Deadpool, would perhaps allow the bodies to live longer? Or a time-manipulator might be able to reverse the effects of his power on the body he's in, sort of 'unwithering it.' Or Kevin could just, as he has in the past, use a Madrox dupe. It's not like he actually *has* to tie up Five business, when there are multiple other solutions available, which they haven't even tried?