For some reason I really don't see that happening. Just can't imagine Wawrinka beating Nadal.
But yeah, he should have taken the second set. It shouldn't even have come to a tiebreak. The same thing happened as in the AO. He owns the first set, then goes up a break in the 2nd only to get broken back at the end of the set. It's a pity. Of course the guy on the other side of the net also had something to do with it.