If you Abort the Mission are you now Out of Formation?
That certainly seems to be what would make sense but I can't see it stated anywhere in either section of the rules.
Will I still receive Fighter Cover on the way back?
The Fighter Cover rule for out of formation B-17s is in Rule 13.2:
"a. A B-17 out of formation within fighter cover range uses fighter cover as per the normal mission procedure."
Sometimes they are the only thing between your B-17 and a watery grave.