The best thing for Trump as a candidate is for both Cruz and Kasich to drop out, but that isn’t going to happen. Kasich will stay forever. If Kasich stays, the best thing for Trump is for Cruz to stay too. That doesn’t guarantee a Trump win, but a three-person race gives Trump the best odds short of both rivals dropping out. Trump voters should not resent Cruz for staying. As a Trump voter who has analyzed more political races than you can imagine, I want Cruz to stay for as long as Kasich does.
It is far more likely that they would support Trump then Kasich or at least sit the primaries out.
You might be right, time will tell.