Considering conservative distrust of Romney was a significant problem six years after he left the governor's mansion, it's probably even more of a problem two years after. His strategy is still probably to swing to the right, turning off moderates, but he certainly picks up less conservative support than McCain did. Therefore I think it's likely he loses even worse than McCain.
The real question then is who does the GOP pick in 2012? There's no other conservative mainstream candidate from OTL, so the establishment would have to find someone else to rally around. Perry came out as a firebrand IOTL and could maybe pivot rhetorically to the middle, but I doubt it. There were about 30 solid speculative candidates, no one very exciting. Certainly one or a few of them would've run if Romney was out, but considering they're second-string Romneys, we have to wonder if this isn't the year a firebrand gets the nomination. From historical events it would appear to be Santorum's year, but I'm also often bullish on Huckabee, if he decides to get into the race. I feel like most of the scenarios where Santorum does well are undermined by the fact that Huckabee will see that, jump in, and steal his base.
While a firebrand candidate is still going to lose in a campaign with the same fundamentals as OTL's 2012, it does change the nature of that loss. We probably see trends in 2012 that reflect what's going to happen in 2016. Pundits realize what's happening among the white working class sooner. 2016 just doesn't end up looking like quite as big a shock.
Perhaps the Democrat in 2016 keys into this and alters strategy enough to counteract it?
I realize a POD of 2008 makes for a different 2016, but stopping the trends that gave us the character of the 2016 election is a bit like stopping a battleship. You need a lot of time and you need to plan early.