There are 2 ways they could return. Way #1 The ran into the mid west bos on the way to cw. mid west bos never heard of them. Enclave couldn t tell mid west bos was bos, because with the right ending to fo tactics the mid west bos would think a lot like Enclave.
So they chat argue about who is more pure human. They test each other find that they both are pure humans. Some Enclave and mid west bos went to cw and to look for tech and be pure humans together but lost , but some Enclave and most mid west bos stayed in Chicago. Enclave learned of their brothers fate in cw and joined with mid west bos who call them selves something else, because they haven t been bos for a long time. They both share the pure human superiority complex, but mid west bos doesn t want to kill mutated humans they want to use them. They use them to fight, work, shovel [censored]. The remaining Enclave are in no position to make demands and just fall in line. High up in the mid west bos. Fo4 Chicago area
Midwestern Brotherhood arn't pure human. Still I can see Enclave remnants on their way to DC making a deal with a like minded group for supplies. Couple of reasons why.
1) The Enclave moving to DC don't have a president. They yet to meet Eden. Not really clear if they knew about Eden before they got to DC.
2 ) Their leader is a military man, Augusts Sir. Coming across a well organised military group with combat Robots, Power Armour and advanced/heavy weapons, would force the Enclave to talk insted of kill. A small group against a large powerful group. Fighting is not really an option. Enclave don't seem to want to fight even when they hold all the advantages.
3) Making a deal would not be so bad. Enclave leave some people behind to man the outpost. Relay station.
4) Enclave get their butts handed to them yet again. They have no power base, no president and no one really can be. They don't have a pot to piss in so to speak. They return to the outpost and have a group meeting. They learn more about Midwestern Brotherhood under Calculator Barnaky. They learn of their war against the Mutant Liberation Army. Barnaky makes them a deal.
"Integrate your remants into my organization. Your leader will be made Elders and given a say. Your scientests will help us upgrade our equipment. Siding with the Midwestern Brotherhood is better then dying slowly in a hole somewhere dreaming of the day when once again you can play the comic book villian only to be destroyed again."
What is left of the Enclave deside "If we can't kill them, might as well control them."
Any other way that brings back the Enclave as a powerful faction would just be stupid.