| Frankly |
They have no crows, right? So they are left with only three options:
1) Sit there and do nothing, keeping the Watchtower strong while the PCs burn villages, torture innocents and kill guards off one by one.
The Paladin would never go for this. He's oathbound to defend the innocent and help the weak. So even if the priest and wizard were smart/cowardly, this would cause the good guys to split THEIR party. When the Paladin is away (to aid a village), the villains can come out and play.
Best case scenario; the PCs will have to fight the lone Paladin without any support backing him up (can possibly stealth-kill him while he's sleeping).
Then, the PCs can go back to whittling away at the Watchtower.
2) Spread out their forces by either:
a) defending the surrounding villages (PC ambush them),
b) sending out runners (which the PCs can intercept),
c) trying to hunt down the PCs (spreading themselves out to catch them)
In all scenarios the good guys get weakened with each encounter.
3) Abandon the Watchtower to do anything under #2, but without spreading out their forces.
They instantly lose their fortified position, leaving the Gestalt Archon behind (it can't leave it's position, remember?) as sole defender and have to choose between getting word out to reinforcements or defending the weak.
No matter what happens, if the PCs are proactive and Evil, they are going to come out on top.