Quote From metabanalysis:
That sounds difficult in admin terms. I think the easiest option would be to find a suitable main supervisor at your current university. If this isn't possible, perhaps you could find an expert at another university who is willing to coach you for the viva. If from another university, this person could be your external supervisor because it would probably be easier to get a new external supervisor than a new university. All of this would be best done before your second supervisor leaves in Sept. It probably wouldn't be difficult to get your second supervisor to continue as your internal supervisor nominally. My guess is that your university might be ok with this setup too i.e. stay at your current university, your second supervisor becomes nominally your main supervisor, and the external supervisor gives you the help you need.