I only just now realized today is Friday, which means no comics for two days.
NOOOOOO *deep breath* OOOOOOO!
Oh crap, you're right!
Which almost certainly means nothing's going to happen in the car, because there's not a good position for a cliffhanger - especially because it's coming off of the wedding arc, which means Jeph's almost certainly going to focus on other characters/arcs.
There's about three variations of one way that I could see him doing the return trip.
All three ways involve him focusing on another storyline for a couple days - Monday and Tuesday, Monday and Wednesday, and Tuesday and Wednesday, most likely, are the three ways. Then, the first of the remaining three days is a conversation in the car, the second is Marten and Claire talking about their past love lives (but mostly just Claire's side being shown, because we've already seen Marten's side - this could serve as massive character development for Claire, too), and Friday would be Marten deciding to become assertive, in a reversal of
564, as the cliffhanger.
If that doesn't happen, I think the return trip won't even be shown - not even showing awkward silence - and other story lines will be shown. And, I don't think that will happen, for the record. #1, Marten hasn't been shown as particularly romantically interested in Claire at all, #2, I don't think Jeph's taking the story in that direction, and #3, Marten's already said in-comic that he considers it unethical to date one of the interns (meaning that it'd have to be Claire making the advance in Friday's comic, and given that #564 already DID that...)
My worst fear right now is that the next strip shows Marten back in Northampton, telling people about his trip to Vermont. But surely Jeph can't be that cruel, can he?
That's what I'm almost certain will happen.