Here's what I think:
Chad & Stephanie Possible to return
Jill & Thomas " "
Nick & Vicki I don't think they are too busy pursuing their careers
Brook & Claire Probably not because of Claire, but I know Brook would go again, even with someone else
Nat & Kat Couldn't get the time off
Gary & Mallory They could probably make it happen
Michael & Kevin Pretty much self-employed, a definite possibility
Katie & Rachel I'm not sure how the beach volleyball circuit works.
Connor & Jonathan I couldn't even venture a guess
Andie & Jenna I don't get from them that they would return
Ron & Tony Have busy careers, Race won't return last place finisher