by Scorpion0x17
That is entirely scenario dependant.In some scenarios you don't even have to exit the map to win, some describe removing the survivors from the board when the reach the exit, some don't, some need one survivor to exit, some all survivors.
In those scenarios where all survivors must exit, I would play it that survivors that have reached the exit zone can stay there, and even return back into the rest of the board, and have to defend themselves, until the remaining survivors make it there, unless the scenario explicitly states that they're removed from the board. And that one can opt to remove any survivor in the exit zone from the board (e.g. to 'bank' supplies), but once removed they may not return.