The Republican Party's new system of having proportional delegates until April means any GOP presidential candidate can make the primary process last for months if they choose to stay in.
Even if front-runner Mitt Romney wins every state going forward, it's unlikely he'll have the delegates necessary to win until April or May — half the delegates won't even be awarded until March 24, and Romney will likely only have half that number of delegates even with strong wins against multiple candidates in the remainder of the upcoming votes.
Ron Paul is clearly in the race for the long haul and has the best campaign structure in the field besides Romney. Newt Gingrich has insisted on staying in through the convention, and Rick Santorum has not shown any signs of dropping out.
Romney's campaign has planned from the start for a long nomination process, is well-organized, has the most money by far and can reactivate 2008 ground operations in states that the other candidates haven't even thought about yet. But even if Romney further cements the perception that he'll be the nominee he'll have to keep campaigning in order to guarantee the delegates necessary for a win.