You're assuming that every voter will go to another candidate. You have no way of knowing what they will do.
I am assuming the majority will go to another candidate. GOP supporters do not see any value in Hillary Clinton and will see Rubio-Kasich as a great alternative....I don't believe Cruz will get people jumping on his boat....he, like trump, likely has maxed out...those that see the value in Cruz, already see the value.
Time will tell....but I think in the end you will see trump with 30%, Cruz with 30% and Rubio with 50%.....