So In the past few weeks Ive done quite a bit of research on Enclave and just so you know Im a huge fan but theres others out there who are bigger fans than me. I have come out to say why the Enclave are still alive and may return some day.
Enclave Return Proof
If you look very closely you will recognize that this is the end of Broken Steel and theres a Vertibird leaving. It has to be an Enclave Vertibird so maybe it was headed for somewhere to be safe and try to gather DC remnants. And theres also ED-E in F:NV who mentions a Chicago outpost for the Enclave so they could make a return for all we know.