Trump needs 57% of the remaining delegates. For him not to get them, Kasich would have to stay in
If Kasich drops out, Cruz DESTROYS Trump going forward. Even if Cruz dropped, Kasich would probably outwin Trump in the remaining contests. Trump is only helped by both of them staying in. He gets closer to 1237 if both stay in than if either drops out.
You don't understand winner-take-all rules or basic math perhaps.
There are two problems with your assertion:
1. It's utterly false, even if Kasich did drop out.
2. Kasich isn't dropping out anytime soon.
Other than that, you're spot on...