What happens when players can't play anymore mid campaign? Just wondering if there has been games in the past when one or more players had to stop playing for some reason and how Acadum handled the situation.

E.g. A 6 player campaign where 2 players for one reason or other can no longer continue.  What happens to the other 4 players in the party? 

Also what if the plot in the game is important to the greater storyline that other games in the living world are also involved in?