Honestly, I don't think the primaries are mattering at all. Every new one is supposed to be the "end," so let's not kid ourselves, we have no idea who will actually be the nominee.
The way I see it, there are basically three possible scenarios right now;
1) By far the most likely - After a much longer than expected primary season, a battered and bruised Romney finally gets the nomination. Some Republicans sigh, shrug, and then try to salvage their party's presidential campaign, while a few are just too uninspired with him and stay home.
2) Less likely, but stranger things have happened - Somehow, through a combination of unlikely factors, Santorum gets the nomination. Many of the GOP higherups are a bit horrified. He wins a few states in the general by a large margin, but overall gets absolutely trounced, as even many current Republicans just can't bring themselves to support him.
3) Unlikely, but with a non-zero chance of happening - No one gets a delegate majority, and the party nominates someone other than the current 4 candidates at the convention. Having to basically start a presidential campaign from scratch with only about two months to the general, this scenario would be an absolute disaster.
My guess; Romney will get the nomination. Somehow, in spite of not being a particularly good choice overall, he has become their safe option.