Build tunnels nearby body of water. Flood section of tunnels with accursed adventures in them. Watch them battered by wall of water, get swept away and separated by currents, and drown (check drowning rules before applying). The clever wizard or sorcerer with the silenced teleport may try to cast, but they'll still need to make a concentration check (a high one, I'd guess) not to mention taking damage every round from battering.
For additional fun, cast silence on barbed arrows (or arrows with tanglefoot bags at the end). Launch at spellcasters, perhaps with assistance of True Strike. Snicker at silenced spellcasters who got no save and must spend an action to pull out arrow.
[Edit: Super Happy Bonus Fun! Use stationary silence spell to block sound of opening gates (blowing walls, what have you) and the rush of water until it is to later. Silence blocks all sounds from moving through the area....enough of these should cover a tunnel.
Later, if there are survivors, use Ghost Sound liberally to create low rumbling water sounds....it should prove amusing.]