I'd rather just see the Enclave in person. They should still be around. Having the Lone Wanderer take down the entire Enclave by him/herself is just ridiculous. I like to believe that they survived and have been regrouping since the end of Fallout 3. That would be a good way to keep the Enclave around. They could be a pretty weak group that can give you missions to help them rebuild. The BoS is going to have little missions for you, so why can't the Enclave?
It's kind of hard, on a deep down logical sense, of thinking they survived, when we as players had to undertake and arrange their complete and utter destruction in the east coast. I mean...sure, we can
retcon what happened in our minds, but that's not going to change what happened.
On the Enclave giving you quests...They're a xenophobic group of military psycho's. They'd kill you before they think of giving you odd jobs.