My big question is how much longer will they hold on?

I expect they will have massive soul searching sessions and come up with a plan for the future.
But then they will ignore it and fall right back into the old pattern because they are still terrified of losing the crazy people votes.
There's no indication that they will break this pattern and start serious governing.

So how long can they last?
Will they regain their conservative votes and put up another mad man? ( I doubt they could ever find anyone else as mad as Trump but they still have some crazy bullets in their gun.)

I guess a lot depends on whether they keep either of the houses.
If they lose both of them I'm sure Hillary won't be as polite as Obama was at the beginning of his term.
She will start driving her agenda through without consulting them at all.
(Remember Obama had special courteous sessions with the Republicans to hear their views before making decisions even though Democrats held both houses. In retrospect, not a good idea.)
Then the GOP will probably be able to rally their forces again, for awhile at least, to fight their common enemy.

But if they hold onto one or both houses, will they just fall back into obstruction as usual for everything Hillary does?

I sure don't know but I don't think the roller coaster is finished yet. We've gone through the biggest, stomach churning drop but we've got a lot more drops to go through before we coast back into the station.