From what I understand they waited in pa that took 0 rads untill it was safe to move to lost hills. I ve never been in the lost hills bunker, but I imagine it to be an air tight goverment hideout that would be stocked with enough food to last the fallout.
The only way to tell would be to dna test them. I don t know if thats been done.
Main point is that if mid west bos has pure humans in their rankes a crippled Enclave would even be more willing to merge with this group on the way to DC.
With the right ending of tactics mid west bos is not bos at all. They quit being bos before they left, becausd they wanted to go against the codex.
If they succeeded, why would they consided themselves bos with any of the endings? They saw the writing on the wall before anyone.
IMO an Enclave/mid west bos merger is totally resonable, and I don t see any reason why at least 50% of current living bos are not pure human.
I d have to take dna samples.