Paul and Gingrich should drop out now. It's about time.
Paul should endorse his pal Romney and Gingrich should endorse Santorum and they should encourage their delegates to vote for Romney or Santorum at the convention (if this is possible).
No, Gingrich shouldn't endorse Santorum. That would just allow his pledged delegates to become free agents, with many of them probably going to Romney. He should suspend his campaign, not endorse anyone else, and hold his delegates in reserve, so that he has leverage, in the event of a brokered convention scenario.