EDF Project FAQ
Q) What! If the map is as big as you say, how can I ever find all the aliens and win the mission? I mean, the colony missions in TFTD were bad, but that ... that would be just plain evil!
A) Well, you can initiate recovery at any time. It's not like XCOM where you had to neutralize all of the aliens before you could end the mission. In fact, neutralizing all of the aliens won't end the mission! You decide when you think there're no more aliens. You press a button to tell your soldiers to initiate recovery ... and if there were still aliens close by, they may well attack and you'll get pulled back into combat. Otherwise, you'll just get warped right to the mission debriefing screen. Neat, eh?
Basically, we should have a Recovery button that we can press when we're fed up of looking for that blasted last alien. The mission should still end when all aliens are dead. But when you couldn't find the last one, you just push the Recovery button and your soldiers will eventually run into the last alien
Of course you wouldn't use this all the time to find aliens because, if there's still many aliens on the battlefield, you'll easily find your soldiers running into dangerous situations for you to handle. After all, the Recovery option wouldn't be smart enough for you to easily "cheat" with it