Technically, no. The Establishment is going to fight Trump tooth and nail, not because they want to stop him so much as they want to either (A) weaken his issue stances they find abhorrent, or (B) actually substitute their own favored candidate out of the blue. (I think they've given up on Cruz; he didn't do what he had to do to convince the Establishment they HAD to ride with him.)
But if Trump wins California and Indiana, I think all this talk of a contested convention will go by the wayside. The greater public will not tolerate the airlifting of a candidate into the convention under those circumstances. At that point, every candidate before Trump was treated as a presumptive nominee, so not doing so would bring out in the open a number of issues the GOP really doesn't want on display during their convention.
If that is, indeed, the case, then it really is over. Doing anything to prop up John Kasich is going to be futile, unless they want him to be the Ngo Dinh Diem of the 2016 RNC. Even if Trump doesn't go in there with 1,237 votes,
who the hell is the GOP going to propose as an alternative? It's clear that the well is poisoned with Cruz and that Kasich lacks any substantive support. Mitt Romney? Paul Ryan? Jeb!?