As a rogue, too often I have managed to get away from a monster, or group of monsters, only to sneak back into that place and have them all come right back after me.
I think that if you manage to lose a monster to the point where they are no longer chasing you and no longer have LOS, that you should lose the aggro from that monster.
It drives me crazy that I can sneak right next to a monster with no problems, but if I open a door, get aggroed, run like hell until I am half way across the map with nothing following me anymore, and then sneak back to the room again, only to have every single thing in there begin attacking me again as though I just ran back in screaming and banging drums.