If the defender has land forces and aircraft with no adjacent territory retreat options, can the aircraft use their flight range to retreat before all defending land forces have been eliminated?
Yes. Defending aircraft can retreat from a territory after any round of combat, even if defending land troops have no place to retreat. [This is similar to the rule that allows attacking aircraft to break off at the beginning of any round of an amphibious assault, even if the attacking amphibious troops do not retreat].
