I think Rossi made a great comeback. Maybe some will say it wasn't that great, but a lot of people thought it was over after Laguna Seca. I actually thought it was over too, but then Hayden failed to finish on the podium and Rossi started reducing the gap race after race. He showed us he never gives up hope and that's what makes him the great champion he is. Of course it's sad for Hayden to (maybe) lose out on the tile this way. Nobody expected Dani to make that kind of move on his teammate, but it happened. I personally think Rossi made a great comeback and imo he's the deserved leader in the title race.
About MS..
If we're being realistic we can assume FA will take the title this season. But then again, this is racing, everything is possible. Nobody expected MS would have an engine failure last GP either. But I just think Fernando will end in the top 8, most likely on the podium, so it doesn't matter what MS will do.
IF somehow FA will fail to finish and MS will win, then for sure it would be a great comeback. Halfway season nobody thought MS would stand a chance. Even if he doesnt win the title, he showed us (like Rossi) that giving up isn't an option. You have to admire that!!