With Romney's operation? Very unlikely.
Even if Santorum were to do about as well as he realistically could do, sweeping most of the south and winning Pennsylvania (unbound delegates, folks) and Texas, Romney would still do well in a few built-in places.
Romney almost certainly wins New York, Connecticut, Massachusetts, California, Oregon, Maryland, D.C., Delaware, Utah, New Jersey, Rhode Island, and Illinois, regardless of how well Santorum is doing (because unless Romney drops out, he will have the money and already has the organization to compete in these places... Santorum will focus on his strengths, as he's done so far). ALL of those states except Massachusetts and Illinois vote after April 1, meaning that they are winner-take-all states.
If Romney won these states here are his "built-in" delegates:
California 169 (+3 "automatic" unbound for party chairman, RNC committee folks)
Connecticut 25 (+3 "automatic"...)
Delaware 17
D.C. 16 (+3 "automatic"...)
Illinois 66 (+3 "automatic"...)
Maryland 37
Massachusetts 38 (+3 "automatic"...)
New Jersey 50
New York 92 (+3 "automatic"...)
Oregon 26 (+3 "automatic"...)
Rhode Island 16 (+3 "automatic"...)
Utah 40
With "automatic" delegates, that's 616 delegates from those states alone, folks. Now granted, Illinois and Massachusetts are both proportional.
Assuming Romney wins 50% of both primaries plus the automatic delegates, he gets 36 from Illinois and 22 from Massachusetts.
Then he has 564 built in delegates, which, given the proportionality for those two states, is a very likely scenario.
Therefore, given that, and the delegates he already has, and the certainty of him winning more delegates in proportional states, the strong likelihood is that Mitt Romney goes to the convention with 800-900 delegates minimum, even in a worst-case-scenario.
Therefore, we should be cheering for Rick Santorum because he will force Mitt to not have the delegates he needs, and make Ron Paul into a kingmaker at the very least, if not an outright convention "compromise candidate," and of course the possibility still exists that we could win the delegates outright.