NPCs
In case you want to try to recruit powerful or otherwise well known NPCs to help, you should know what's available.
In town:
Fred Foster, bard, famous soldier
Greg Barkley, soldier, friend of Fred
Mayor Richards, aristocrat
Rainold Garook, human sorcerer. Able to cast Disintegrate.
Brian Porter, priest of Cuthbert. Able to cast Raise Dead.
In Bylan:
You could probably find a mid to high level member of just about any class among the cities in Bylan, though not necessarily together. Assume you would know where to teleport to to find an NPC in at least one such class. The PC party is considered the most powerful group of adventurers in Bylan.
In the world:
Cellon: The elves are known for their powerful wizards and may be willing to help, but they have suffered great losses in their war against the drow and have no desire to enter another war.
Chovia: The lands of the dark-skinned folk are dominated by the Serrans, who left Bylan as part of the agreement that ended the war. The Serrans are known for their use of mind control, especially by way of a virus that lets them do it more easily, and for their power over dragons. They suffered great losses in the war but probably still have considerable resources. While evil, they have sometimes been fairly good rulers and might be willing to deal in order to gain a foothold back in Bylan.
Sasog: The Sasoguese unearthed the Tarrasque and would know more about it than anyone else. They are known for their powerful liches. While certainly evil they might help in exchange for something of great value - most likely, Haessellekh.
Shar: The yaun-ti have suffered considerable losses and are always looking to expand their power. Any help would come at some great price, if it could be obtained at all.