When Professor Jacob Seltzman used his mind-exchange technology to perform a three way exchange between himself, the Colonel, and 'The Prisoner', Seltzman put his mind into the body of the Colonel and was able to make his escape from "The Village". It could be that Seltzman decided to hide in plain sight in order to avoid those who would force him to continue his research for their own corrupted goals. If so, he could have assumed the identity of a "Professor Hayter" to go with his new body. As such, he may have taken a position at Darlington where he could conduct research on perceptual conditioning, which for him would probably be a rather non-taxing pursuit. (Mentally, he would probably still feel all of his years as well as the effects of the recent traumatic events in his life; and this line of work would have been quite easy for him.) In 1982, Professor Hayter was on board a Concorde Flight which was "temporally hijacked" by a Gallifreyan Time Lord known as "The Master". Perhaps due to his mind transfer, Professor Hayter was able to withstand the hypnosis imposed on the other passengers.
Stranded in the prehistoric past, Hayter joined forces with another Time Lord, one who was known as "The Doctor". Ultimately, Hayter sacrificed his physical life to the Xeraphin Gestalt in order to gain total scientific knowledge. (A similar fate would befall Lt. Ilia and Commander Willard Decker several hundred years into our future.) Although his physical presence had "died", Professor Hayter lived on as a spiritual being and even came back long enough to help defeat the Master's plans.
SHOWS [& MOVIES] CITED:
'The Prisoner' - "Do Not Forsake Me, Oh My Darling"
'Doctor Who' - "Time-Flight"
"Star Trek: The Motion Picture"
[Nigel Stock played the Colonel/Professor Seltzman in 'The Prisoner' - "Do Not Forsake Me Oh My Darling" and he played Professor Hayter in 'Doctor Who' - "Time-Flight"]