WG. I can't see how they can return, we're getting no net increase in jets until 2018 so unless they move an E175 to EXT or fly them as through routes, both of which seem unviable, then there probably isn't a return for them.
However, just thinking out loud here. Is the 4th rotation to Manchester being operated from Manchester with a 175? If so then there could be a chance there, which is a contradiction to what I've just typed above. Either way I can't see a based jet in Exeter for the foreseeable future.