Before I start I've searched for all threads under "av" "despawn" "archers" and haven't found anything similar listed.
As a rogue, when you go to attack a tower in AV...
-Start by sapping one of the archers
-Go around and cap the flag without aggroing
-As soon as the tower goes contested all the archers
Archers are gone for good, even if alliance retake the tower.
I found this is especially helpful for Dun Baldar North and South as it allows your team to fight further up without having to worry about archers.