Here’s an idea. Vicki stays onboard the Tardis after The Myth Makers and takes up Katarina’s role in The Daleks’ Masterplan. As it stands, Katarina, despite having massive potential, is wasted and serves no purpose in the story. Since we’d be working with recons, swapping out characters shouldn’t be too hard.

Speaking of Masterplan, based on the title, I came to realize Mavic Chen being the Master would actually feel really appropriate. Just add a line or two stating this and there you go. The actor who plays him also plays a similar villain-assisting role in The Invasion as Tobias Vaughn. I haven’t seen it yet, but perhaps that could be that same Master, and he was just using a disguise in Masterplan, something the Master has been known to do. I guess thanks to being mostly recons, you could just make Chen look like Vaughn, but then what would you do for the episodes that aren’t missing?

Something brilliant I’ve seen done is having the faces offered to the Second Doctor in The War Games be his future incarnations.