I don't agree. These people will eventually see it is him or Hillary, who they irrationally hate, and will all fall in line.
If Cruz or Trump have the candidacy stolen by someone who won one state, they'll just straight up start campaigning against Kasich. It'll be a GOP civil war. Neither are going to just sit back and tell their supporters to vote for Kasich, neither really care at all about party loyalty and have no reason not to just burn the whole thing down, since they got cheated.
It's different than the Bernie or Bust crowd, because for them, you can point out that "hey, Hillary won the popular vote and had the most delegates" and eventually they'll come around to that idea because nothing really wrong or foul went on (beyond conspiracy theories).
With Kasich, something foul will have gone on, and arguments against not supporting him will be well founded.
Kasich also can't win on his base alone. He has to court some independents, minorities, and even some Democrats (like Bush did), and stealing the election from Trump or Cruz wouldn't do that at all.