He still would've won, but McCain probably would have won Indiana, North Carolina, Virginia, Florida, and Nebraska 02. In terms of the popular vote, Obama wins by around 3-4%.
A lot of people talk about Obama's numbers going down in his re-election bid, but Obama's 2008 win was inflated in the first place. People thought the financial collapse was a 1929-level event and wanted to punish the GOP at the time. Obama won by 4% in 2012, because his numbers went up from what they would've been had he won without the financial collapse, which would've been as close as 2000, 1-2%.
He would've had a good chance of losing OH too. His electoral barrier was NV, CO and IA thanks to his ground game in those states. Mccain actually had a very good chance to win if he could've pulled off NH. Palin was picked to help him with consolidating the base and picking off PUMAs in states like NH.
Palin was doing quite fine until the Couric interview about the bailouts, which Mccain himself was confused about supporting, but this again, happened only in the context of the financial crisis.
Mccain had better odds of beating Obama in 2008 than Romney ever did in 2012. Bush/Paulson screwed him over by trusting the UK with Barclays merger, they pulled out at the last minute.