I really can't see Rob jumping back to the Barbie Twins. His best case scenario is to take one of them to Final 2, thereby nullyifing their vote against him on the jury.
At this point, Alex and either Jenna/Heidi is a lost cause.
He MIGHT have Deena and or Dave's vote and the other three are a guarantee. (Matt, Butch and Christy - I can't see any of them voting for Heidi or Jenna)