4. Recasting
The Five Doctors had to go this way and recast William Hartnell with Richard Hurndall (pictured) to mixed reception from fans. Although this might, therefore, seem like a dangerous way forward there is a lot of speculation concerning the possibility of David Bradley taking the part. The logic is this:
David Bradley is playing the part of William Hartnell in the Mark Gatiss drama An Adventure In Time And Space; viewers will get used to seeing him as the First Doctor and will not be as distressed when he turns up in the special. I think this is not impossible and would rate this as a 50% possibility.