To be honest, I’m not sure I’d like to see XF coming back without Gillian. Watching the seasons without David was painful and I don’t want to revive this again. This show is about Mulder and Scully for me so if you remove one of the main character, it loses its essence. I’d watch it, of course, but that would be painful.
However, I don’t believe Chris and David would be up to do more without her and even if they were, with those bad ratings that are dropping every week, there’s very little chance that Fox and Disney will want to do another season.
At this point, I think Gillian is even making it easier for Fox so they don’t have to “cancel” the show due to the low ratings, which is what they would probably do if Gillian finally changed her mind.