At the end of ‘The Three Doctors’ the Time Lords provide the Doctor with a new dematerialisation circuit and restore his knowledge of time travel. Once again the Doctor is free to explore space and time.
How would things change if they didn’t? What if the Doctor had continued his exile on Earth?
While the space based stories would vanish from the timeline (Carnival of Monsters, Frontier in Space, Planet of the Daleks) other UNIT based stories would still happen.
‘The Green Death’ would have more involvement from the Doctor, since he doesn’t take his short trip to Metebelis Three (and most importantly doesn’t take a crystal that will lead to ‘Planet of the Spiders’).
‘The Time Warrior’ is trickier as the Doctor uses the TARDIS to the middle ages. It can still occur as Linx was using a Osmic Projector to snatch scientists from the 20th century. If the Doctor was able to work this out he could use himself as bait and allow himself to be taken back in time.
Once in the Middle Ages the Doctor need only reverse the Osmic Projector to return everyone to their rightful place in time. The only change is that Sarah Jane Smith would have had only a minor role and as a consequence may have no further interaction with the Doctor or UNIT.
The ‘Invasion of the Dinosaurs’ could have the Doctor on hand when the first time distortions but it is an easy tweak for the Doctor to arrive back from the Middle Ages once events are in motion, just as occurs in the original story.
Without the removal of their blue crystal the spiders of Metebelis Three don’t come to Earth and destroy themselves when the Spider Queen tries to extend her powers. Blissfully unaware the Doctor continues to live out his current incarnation on Earth.
‘Robot’ and ‘Terror of the Zygons’ fit perfectly as Third Doctor adventures. The lack of alien invasions and the decline of UNIT would give the Doctor time to pursue his own interests.
Would he continue to try and get the TARDIS to work or would he eventually accept his fate? Would he even make a deal with the devil by teaming up with the Master (who has kept his activities restricted to Earth since he knows the Doctor can’t challenge him anywhere else)?
Let us suppose that the Doctor eventually does regenerate on Earth. How would being exiled effect the Fourth Doctor? I would suggest that he wouldn’t restrict himself to the UK and begin travelling the globe. This fits perfectly with a Doctor who enjoys spending time in Paris and Italy.
He’d still be on call if UNIT needed him but I think the Fourth Doctor would relish his independence. He’d pick up travelling companions along the way, giving them a guided tour of their own world.
This is a perfect setup for an International flavoured campaign set on ‘modern day’ Earth. A traveller of no fixed abode, seeing the sights and getting into trouble. There is so much to explore that the Doctor might not even mind that he is confined to one world, at least for a few centuries.
The campaign can almost become a travelogue. Companions could be made up of locals or tourists, especially students on their gap year. The Doctor is unlikely to form any deep bonds with them. He’d make it clear that this is a temporary arrangement and that he has no intention of settling down. For the moment they can walk the same path but tomorrow he’ll be moving on.
Adventures don’t have to involve any science fiction elements. Other countries and cultures are as exotic as any alien world. There are wonders, danger and excitement to be found everywhere.
Not to say that the Doctor won’t encounter aliens or time travellers. Why would these outsiders restrict themselves to the UK? The Doctor could be on hand to prevent aliens from escaping their prison beneath the sphinx in Egypt, foil a time travellers attempt to plunge Sweden back into the prehistoric era or discover the secret alien invasion in the heart of Amazon.
The Doctor’s time line could end up back on track with ‘The Ribos Operation’. The White Guardian could recruit the Doctor in exchange for use of his TARDIS or they could use a time capsule owned by Romana.
Events could proceed as before, with the Doctor embracing his ability to explore space and time once again. Alternatively he might have gained a deeper appreciation for Earth and return there, gaining more fulfilment by travelling by more primitive forms of transport than the TARDIS.
He might pass this passion on to Romana. At last he would have a companion who can stay with him forever on his travels. With two Time Lords in permanent residence Earth would enjoy a great deal of protection.
Occasionally they might send a postcard to Gallifrey with a simple message.
‘Wish You Were Here!’