Didn't they include this kind of advice with random encounters in the Blingdenstone adventure in the playtest package. I think I remember them specifically saying that there were X amount of orcs so if they are encountered outside of their camp keep track of it. They also explained that if over y amount of orcs were killed outside the camp, then the entire clan of orcs would fall back and be more defensive, getting ready for attacks. (I think that's what it mentioned).
This type of advice allows for wandering monsters that make sense in a campaign setting. It works great.
It might have in that adventure, but in the packet it glosses over it and in other adventures it also glosses over it.
But I also think you're looking for rules and guidelines in the wrong place. In AD&D, for instance, the DMG has a discussion of what can be involved in clearing an area of monsters so that no more random encounters will occur. To some extent its common sense advice, but in a game where players are expected, at high level, to have their PCs clear out monsters and build a castle it makes sense to have some details.
Can you point me to the page number that is on, because I'm currently converting a 1E adventure to 4E and I can't figure out how many random encounters should convert to static encounters because it doesn't list it anywhere.