Rubio has no chance if Cruz and Trump both have more delegates than he does.
In the case of Trump or Cruz the likely winner is the delegate with the most votes. Can Cruz win over Tump delegates if they are released by Trump. I think so. And the opposite holds true as well.
You’re correct. Using your numbers, even remembering about 15% of the delegates are uncommitted “superdelegates” it belongs to Trump and Cruz to work it out. The fear than Jeb and supporters in the RNC can work something out here is baseless at this point. Personally, while things can change dramatically, I don’t see Jeb rallying to 40% which is probably where he’d need to get.