Question about the Great Valley...HELP!!!

If the Great Valley is supposed to be Heaven and the entire movie is the gangs journey into purgatory and Heaven with the guidance of Littlefoot's mothers prayers, then how come at the end, Littefoot's mother isn't there? She said she's never seen the Great Valley.

Also, where are Spike's parents? They weren't at the Great Valley at the end. Neither was Littlefoot's father. Where was he?

And, if they're all supposed to be dead, how did they all die? It never showed them dying.

I love this movie, I'm just wondering because I never thought anything about the Great Valley being Heaven until just last night when I watched it again and came on here to read about it.
*Stevee*

T~O