Greb doesn't tear him up. Schmeling will land clever counter right hands to a decision victory. Hard to call of course because of the lack of footage, but i think the German is too big and skilled to overcome.
I think much depends on what each fighter knows about the other and their level of preparation. If Schmeling comes in planing to try to box Greb at long range like Gene Tunney did first time round he will get his a55 handed to him. If he uses a better thought out strategy like Tommy Loughran did he would win.
Loughran was the guy who got Grebs number first time round. He created the strategy of "sustained body attack" forcing Greb back, that was alien to his usual aproach. Gene Tunney latter adopted this strategy to win the latter fights of his series with Greb. Smart guy Loughran.