Because the other clans drove Skyclan out.
I don't think Snowkit will ever come back.
snowkit
Snowkit was carried off by a hawk because he was deaf and he couldn't hear the hawk and his mother, Speckletail.
Nobody hated Snowkit. They were just a bit surprised that he was deaf and didn't know what to do with him.
a hawk killed him
In the book Bluestar's prophecy she is but the next one is a boy.
She went to starclan since in the lost warrior she is seen in starclan with Silverstream.
She's dead, but it is not know whether she is in StarClan. She probably is in StarClan. She didn't do anything that's Dark-Forest-bad.
Yes, when Honeyfern died she went to Starclan.
oakheart came and brought her to starclan.
If the cats are good even if they don't believe in StarClan they go to StarClan, but the cats like the cats from BloodClan don't. I'm not sure about the cats that have never heard of StarClan, but are good. Even if some cats believe in StarClan, but they do some really bad things, then they go to the "Place of No Stars".
Yes. As far as we know, Snowkit is dead. Despite this, there have been many fan fiction stories written by fans of the series about Snowkit returning to the clans, or surviving and going on an adventure of some sort. You can find many of these stories on fanfiction.com.