I think Max ending up in Heaven would only occur if (a) Sam was there with him. Otherwise, he'd only end up being in his own personal Hell anyway. I say that their reward in Heaven is that both of them become demons and get to terrorize the Hell offices as much as they please.
I am a community moderator, here to assist, keep the peace, and keep these boards clean and friendly for all. I am a volunteer, and not a Telltale employee, and my opinions are my own.
--Playin' poker with GLaDOS before it was cool--