Well that is a good hypothetical look at what some poll says but actual results show that as more and more candidates drop out, Trump continues to win. He is getting a portion of the support from each of the candidates that drop out.
Also Trump seems close to 35% as his ceiling. I know he gets more in some states, fewer votes in others, but to me that seems like his ceiling.
Secondly look at the two candidates who will drop out.
Rubio - seems very aligned with Cruz except on immigration. I would bet the huge majority would go to Cruz. That is what the polls say.
Kasich - He is different. he is actually the consummate liberal country club republican. His supporters would be sick thinking of voting for either Trump or Cruz. My take here is they don't vote, or vote more for Cruz as they are horrified by Trumps antics.
This is why the Cruz campaign starts in earnest next Wednesday. Mano y mano.
I will say if Cruz dropped out the majority of his supporters would go to Trump.