I like to think, when he sleeps, Simon subconsciously recites Russian Orthodox prayers, and Marcy recites them with him. I wonder if Simon gave her the Madonna and child Icon. Wouldn't it be ironic if one of the last conscious Christians was a Vampire?
Meanwhile, in an alternate universe, Marceline the Rockstar goes to visit her grandfather in the nursing home. The man raised her and is now going through Alzheimer's and therefore barely remembers anyone or anything, let alone himself. He only remembers a hand full of fragments, shadows really, of his wife, and his granddaughter.
The firework comment is a very nice touch. A memory of a memory perhaps but hes still in there SOMEWHERE.
But honestly what I would love to see on the show is an enraged Ice King vs The Lich. I mean, how often does simon take himself seriously enough to show what kind of power he actually has. I honestly think he holds back a lot.