They will make some type of excuse for why they're not there. They said for vicki something about how she hadn't forgiven Den for what he said at christmas.
There isn't really a point in them coming back. They weren't major characters or anything. It would have been nice though to have had Alfie, Kat, Jake, Danny, Spencer, Maxwell all at the funeral. The moons reunited. I don;t see it happening though
xxx
Hiro: ...but you flying man! WHOOOOSSSHHH!
Nathan: Would you keep it down?
Hiro: ...whooooosh.