Well, we can assume that in 1990 or 1991, depending on how long the BBC twiddles its thumbs, the show comes back. Let's say, for the sake of argument, in 1991. Same production team as before, with an additional three episodes added to the season to allow for the production of the Seventh Doctor's regeneration story.
Earth Aid premieres on BBC1 at 7.25 on Sept. 7th, which is followed by Ice Time, cuing Ace's departure to become a Time Lord (as was planned). From there, Raine Cunningham joins the TARDIS crew in the following story - Crime of the Century. The next story is Night Thoughts (later adapted for Big Finish), and the season wraps up with the Seventh Doctor's regeneration story, Alixion.
Earth Aid - by Ben Aaronovitch - 3 parts
Ice Time - by Marc Platt - 4 parts
Crime of the Century - by Ben Aaronovitch - 4 parts
Night Thoughts - by Edward Young - 3 parts
Alixion - by Robin Mukherjee - 3 parts
From here things get murky, but we can assume the Eighth Doctor's first season would look something like this, assuming there were an order for 20 episodes. Let's also assume that Marc Platt has taken over as script editor.
Network - by Ben Aaronovitch (and Marc Platt, uncredited ) - 4 episodes
Animal - by Andrew Cartmel - 4 episodes
Hostage - by Neil Penswick - 3 episodes
A School for Glory - by Tony Etchells and (Unknown co-writer) - 2 episodes
Avatar - by David A. McIntee - 3 episodes
Illegal Alien - by Mike Tucker - 4 episodes
This is, of course, mainly well-inferred guesswork for Season 28 here.
As for the Eighth Doctor? Richard Griffiths, Robert Hardy, and perhaps John Thaw all stick out as being clear choices. At least to me. Maybe Ben Kingsley?