Perhaps later; right now, John's got to be a dick.
Panel 1: We start the proceedings with John packing his suitcase. As a glum Elly looks on, he says he's glad she doesn't mind his taking off like this.
Panel 2: He points out that she could have come with him but that would mean they'd have to find someone to take the kids.
Panel 3: He them tries to soften the blow of her having to be stuck with the kids he "knows" she wants to escape from by pointing out that conventions are nothing more than standing around, listening to boring lectures and making chit-chat.
Panel 4: As he makes to kiss her good-bye he says she wouldn't have enjoyed it anyway.
Panel 5: Elly, who "knew" all along that she wouldn't have been required to attend the damned convention, responds to the loss of an opportunity to see new things and escape drudgery and short people who ask her stupid questions like "Do you love me, Mommy?" and talk about stupid things like how they feel (like THAT matters) by blowing a reapberry.
Summary: The official version of the punchline is "Not only is John being a patronizing wad of shit who wants to shackle Elly to the house, he's trying to fool her into thinking he's not going to cheat." The more realistic version is that John remembers what a drag Elly was the last time they vacationed without the kids; also, if he could being himself to trust Connie or Annie and could be free and inhuman like Elly and ignore the crying of children who think they're being abandoned forever, he'd take a child free vacation. Too bad that he does become as heartless as Elly. It'll make April's life suck.