There is a limit of 100 deceased followers that can lie in the Graveyard. Once the limit of 100 is reached, the first follower that entered is forever forgotten into oblivion.
This is the only limit, as long as there is less than 100 deceased followers in the Graveyard they can stay there for as long as necessary.
As far as I know no post should have been deleted from the forum. Could you please tell when or what posts are missing?