There is a 46% chance of a second ballot. There is 74% likelihood that Donald Trump wins the nomination, 13% for Ted Cruz, and 11% for John Kasich. Assume that Trump is the only person that can win nomination on the first ballot. Here is a quick and dirty estimate to consider:
54% that Trump wins on the first ballot
20% that Trump wins on the second or more ballot
13% that Cruz wins on the second or more ballot
11% that Kasich wins on the second or more ballot
1% that Paul Ryan wins on the second or more ballot
Which means Trump is about 45% to win, should the nomination be contested. And, if not, he is about 50% likely to try to run as an independent or minor party candidate.