Ok, here is the deal regarding both your questions(which have received several erroneous answers):
1. You can NOT retreat before a combat has begun. In phase 3 you make your combat moves, ie. move your chips around or write in a post: “combat moves as follows…” THEN in phase 4 you conduct all these combats, meaning you have to roll for at least 1 round of combat before you are given the option to retreat.
PHASE 4: CONDUCT COMBAT
In this phase, you resolve combat in each space that contains your units and units from the opposing side. Complete all combat moves before resolving any combat. (An exception is an amphibious assault, in which sea combat must be handled before land combat. See “Special Combats” for more information.)
2. If an attacker retreats or is destroyed in a naval battle leaving the defending fighters alive these fighters can move 1 space to a friendly territory to land. This fighter will “hover” in the sea zone until the end of non-combat move phase, in which it must land or be destroyed.
So in your case those fighers can not participate in the defense of FIC in addition to defending the sea zone. Furthermore, they will drop from the skies and sink if you manage to capture FIC. (Unless he has another AC in one of the surrounding sea zones) Good move!