Leavers

1) If person didn't leave on purpose (NetErr, computer freeze) after they log back on, if they party is still on mission/quest they can be prompted to rejoin.
I don't know is this is already been suggested, if it is then ignory it.

2) When someone leaves they are replaces with similar hench and party can go on without missing people.

I like the idea of a Replacement Fighter in case of a dropped player.

That seems like a good idea if it could be implemented.

solution #1 should be implemented ... totally agreed

if the instance is closed on leaving neither you or a hacker can get back in