It means you have to keep on inventing random encounters.
Clearing out the forest of the evil magics at its heart -- learning that all sorts of evil things battened on to the source and even those consumed by it may have left unpleasant surprises is a nice dramatic twist, but does mean you need all sorts of evil things to plague the characters.
Or the subtle and evil mastermind conclude that they had best deal with the hero at arm's length, and specifically choose attackers that would not lead back to them. (Though the hero will deduce that he's facing too much to plausibly be actual random attacks. Only so much you can do when he keeps bringing them down)