I think that Oscar fought the best possible fight he could the first time and it wasnt quite enough. Hes not going to be better in the rematch, especially if hes weight drained. His only chance for victory is that Mayweather doesnt fight as good as he did the first time and starts to slip himself.
In answer to the question, if Floyd loses, it depends how he loses and how Oscar looks winning. First Oscar needs to look good against Forbes. I think Forbes will probably lose but make Oscar look pretty bad in doing so.