Tammy isn't dumb. She won't dedicate the rest of her life to wiping Jack's ass and throwing out her back trying to pick him up.
Eh, you never know. Tammy seems to be okay with being saddled with the load. #EverybodyNeedsATammy, right?
If she’s tolerated it thus far, I can see her sticking it out until the end. She originally married Jack because she saw him as a man with tremendous potential for success, and felt that he was destined to do great things.
She’s watched as those dreams have effectively evaporated in front of her eyes. 26 years of marriage (they were married in 1997, I think), and she has nothing good to show for it, other than being a tertiary character in her Z-list “celebrity” lolcow husband’s internet idiocy that has vacillated between clown show, to horror show, to death watch. She could’ve gotten out sooner if she wanted, since she’s not stupid enough to be totally oblivious to the fact that Jack’s condition would continue to deteriorate.
Unless she has plans to radically remake herself and pursue a different path with the time she has left,
what else does she have? It’s almost as if she’s spent a lot of time (26 years) watching a bad movie, but is too far into it to shut it off. There’s too much investment that, despite not liking it, it’d be even more of a waste to switch it off without at least seeing it through to the ending.
Tammy has no purpose, and coupled with her religious belief, I’m left to agree with
@charlesdickens 
.
Tammy could see it as a Christian wifely duties or something. God points.