Kids who become
adults what happens to them?
Long and spoilery answer...
They age rapidly and die.
The virus "comes back" in season 1 and 2, but they develop an antidote, but after a while, the virus dies off and isn't a threat anymore.
But at the end of Season/Series 5 a new virus is released, but there was no season 6 to deal with that.
Then how is the tribe good since every one has to die? real world no one is going to live forever.
so the tribe is cancelled?
Then how would they deal with actors who aged out of there characters?
Kill them off?
The virus either has disappeared, or everyone is now immune to it.
The "new" virus at the end of Season/series 5 never got fully explained, but it is implied that it will only affect the city and not go global like the original virus.
The show was cancelled after season 5, so there is no formal answer to how it works. Apparently there are two scripts floating around the interwebs from the not-produced season 6.
how much of the main cast was still there in season 5?
well it still doesnt make sense since they have to grow up
Not sure why you are upset at them growing up...the virus isn't an issue anymmore...But yes, Ebony is probably 15 in season 1, and 19 or 20 in season 5...but she is still badass.
But as for original cast, off the top of my head, the people from season 1 that are in season 5 are:
Amber, Trudy, Jack, Ellie, Ebony, Lex, Trudy's baby and Salene.