I think it’s absolutely possible. Depends on the new OC. I think Diaz needed to clear the decks so that the new OC wouldn’t feel obligated. Having staff in place would only complicate the search. If the new OC feels that Hartley, for example, is the best TE coach/recruiter available, there’s no reason they couldn’t hire him back.
Personally, I think they are all completely replaceable. I would personally welcome Hartley back, but DGAF if he’s gone for good either. Dugans I would somewhat warily accept. Anyone else comes back I’ll be ****ed.