What will happen once after a fork, every decides to leave/sell out their bitcoin for the forked alt. Whatever the reason, whichever the fork and outcome name, would that be the end of bitcoin? How will the btc value be afterwards?
And how would the miners react to it?
It depends whether you believe Bitcoin can hard fork and still remain "Bitcoin." Technically, when a hard fork occurs, a new altcoin is always being created, and the hope of the fork developers is that users of the legacy chain will switch to the altcoin. If there is widespread disagreement over the name "Bitcoin" then I think the legacy chain should retain the name, because that is
technically correct, as the new coin is an altcoin.
This raises important questions... would "everyone" really ever leave Bitcoin for an alt? I think this would only happen if a truly existential protocol flaw were discovered. If that happened, I think there would be wide agreement to fork.