1) Milk it - come out guns blazing, i'm going to repeal it, etc.
2) Try like hell to raise a lot of money out of it.
3) Wait a week or two, then quietly move the dialogue back to "We need jobs!"
By election day, most americans will realize this is now the law of the land, endorsed by John Roberts. Romney can't run for re-election if he fails to repeal obamacare - and the facts are, he can only approve congress' bills on it (just like how it was APPROVED by a repub congress too...)
So I think he'll milk it, and then get very quiet about the issue.