If Cruz has still have any brains left (never mind decency), he will come and support Trump enthusiastically — for his own future.
You are right
I predict that Cruz, Bush, Ryan, Rubio, Romney, Graham, et al will all stay neutral on the off chance that Trump will be a disaster and try to salvage what scraps are left of the party. Unfortunately for them, they will be but mere grainy, black and white thoughts that go the way of the Whigs as Trump schlongs Hillary in a landslide and has one hell of a roller coaster one term. Yes, I believe it will only be one term. Trump will be itching to get back to golf and his business after turning the out of control cruise ship around.