That's what usually happens. He isn't a complete fool. Sure, he'd move toward the center, just as the Democratic nominee will. But I'm not sure he'd be able to control himself. Right now, even with some big wins, he's calling people "disgusting". He just can't resist.
And if he does moderate his tone, and stops devoting half of every speech to insults, he'll have to offer and explain some serious policies. And I think that would be difficult for him.