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?
You are stating a scenario which will never going to happen, well let suppose it happens then surely the bitcoin will fall down rapidly because the investors will shift their money to that altcoin. Miners will do the same, they will start mining that other altcoin.