Thing is, preparing for combat against them doesn't make a heck of a lot of RP sense. Trusting Lae'zel aside, we don't have any way of knowing that the dragon and its rider are going to run away at the start of the fight. With them still around for the fight, we're toast. Literally.
On the contrary ... its makes perfect sence, you send up your emissary (protagonist, and Lae'zel preferably), yet you prepare backup if something went wrong ... or you dont, and then suffer the consequences.

Yes, i know there is a big dragon ... wich seem to me like just another reason to prepare backup.