I prefer Rick, but even if I didn’t I think that this is a reasonable decision. It’s still early. Only a very small percentage of the delegates have been selected. If it looks like his remaining in the race will throw it to Romney, I would assume that Rick will exit. But Newt is somewhat of a loose cannon, and he has some baggage—both personally and ideologically. If he proves unpopular with the general public, it would be good to have a fallback position in Rick.
It’s reasonable to conclude that Newt’s roller-coaster ride will continue until either the convention, or until he calls it quits because of the math.
Though giving up half its delegates to do be, FL is "winner take all" so a win for Romney reestablishes his momentum going into a certain win in Mormon-heavy Nevada caucus.
It's likely the Maine, Colorado caucuses will be Romney territory as well; the Missouri primary doesn't determine their delegates (that's done in a March caucus) to it's technically irrelevant.
Michigan is Romney's birth state and his dad was governor; he'll win easily--Santorum's focus on manufacturing won't help there. As a result of the calendar, after FL, AZ is the next "obvious" competitive state and it's vote is more than a month from now, just before Super Tuesday.
Santorum can wait around like a vulture hoping to see Newt stumble, siphoning off delegates and helping Romney or exit ahead of FL and maybe help prevent Romney from that big prize which restores his momentum and the story of inevitability.
This week is a time for choosing for the Senator. Is he a willing tool of the establishment (like in Thune vs. Spector) or does he care more about his issues?
If the race was just Newt vs. Santorum, I'd be all for it but that isn't happening. Santorum's persistence can only assist Romney's rebound. If Santorum really truly believes Newt is that unstable, too great a risk, that Newt will eventually flame out, Rick should drop and endorse Romney.