The only way Romney doesn't survive March is if somebody pulls a Brutus on him. This article is insane, implying that Romney's going to have a hard three weeks after last night's results. Mr. Chalian may have missed it, but Santorum's extremely narrow wins in Mississippi and Alabama gave him all of 8 more delegates than Romney; Romney more than wiped that out with American Samoa's 9 delegates, plus Hawaii.
And where are we going next? Puerto Rico, which is winner take all. I'd bet good money Romney will win that on Sunday. So whatever momentum Santorum got from yesterday (and really, it shouldn't be much, he needed to do much better than that in the South to keep this race close) will be gone before next Tuesday.
After that, outside of Louisiana and Pennsylvania, I don't see Santorum winning any other states. During that same stretch, Romney will likely pick up Maryland, D.C., Wisconsin, Deleware, and Connecticut in winner take all matches, while also dominating New York and Rhode Island.
And again, this primary ends with winner take all in California, New Jersey, and Utah, where Romney will pick up 260 delegates to Santorum's zero. Based on a very rough projection of the remaining races, I think Romney will need about 100 of the unpledged delegates to secure nomination. That's roughly a third of them.
The media can try to spin this as a rough time for Romney all they want; I believe it's effectively over.