Thornir Alekeg
Albatross!
The way I see it, there would likely be some of the guard that need direction, and look to the PCs to provide it. There would be others who would dislike the fact that the PCs are not part of the guard, and would be opposed to the PCs appearing to usurp the command structure no matter what the Captain asked of the PCs. As a result, I would expect that some of the guardsmen would be wanting to join the PCs to help take on the goblin threat, while others would be glad to see them go.
Depending upon how you play Corporal Carl, he would either make his case for why the PCs should stay in town to help defend it, as per the captain's request, or he would be fine with the PCs leaving, but and would quickly try to assert his authority to make sure all the remaining guards stay and don't follow the PCs on some damn fool mission.
Depending upon how you play Corporal Carl, he would either make his case for why the PCs should stay in town to help defend it, as per the captain's request, or he would be fine with the PCs leaving, but and would quickly try to assert his authority to make sure all the remaining guards stay and don't follow the PCs on some damn fool mission.