I think it's a lot less complex than that. The play is that if the seat if vacant there's always the possibility that a group of Republicans might crossover and offer the Democrats something or someone worth voting for. It's a calculated risk that the seat won't move further to the right but even if it does there's still the Senate and White House as a backstop.
Is it likely? No. Is it possible? Sure. As giddy as this thread is about a potential speaker Trump I'd say his nomination would make it more likely.
That being said I agree that the game of chicken with a functioning government is getting tiresome.