Christmas is pretty much a secular holiday at this point anyway. I don't understand why we don't just completely remove the 'Christ' part and have two different holidays- one to remember Jesus and celebrate his birth, and another to give gifts to each other as a sign of affection and community. Keep 'Decemberween', as it shall be called, on Dec 25, and have Jesus' birthday celebration on his actual birthday, which I think is sometime in September?
So no, if Jesus did return and disliked Christmas, I'd still celebrate it. Granted, I'd probably be way too busy dealing with the Earth-shattering revelation that the Judeo-Christian God actually exists, but still.