Mr Dexter, who wrote the Inspector Morse novels, has said there should be no remakes of the Morse TV episodes featuring John Thaw.
In Endeavour, the Inspector Morse prequel, Mr Evans plays Morse as a young detective in the 1960s but he said it was unlikely that the series would carry on into the 1970s because it would then move into the period of Morse’s career played by Mr Thaw, before his death from cancer in 2002.
Endeavour made its debut with a feature-length special in 2012, which led to two series.
Author Colin Dexter has insisted there can be no remakes of the Inspector Morse episodes starring Mr Thaw, and Mr Evans said: “I know that Colin has it in his will that no one else can play the part, which is as it should be.
“It’s not something that can go on and on. I really don’t think it will.”
The second series of Endeavour follows the detective constable’s early career in Oxford during the mid-1960s.
Mr Evans was speaking to the Radio Times as the Morse spin-off returned to Oxford this week for filming for its eighth season.
Asked whether viewers could expect to see the drama move into the 1970s, Mr Evans said: “Listen, never say never.
“It would be a great life for me, I suppose. But is it something you’d want, creatively? I’m not so sure.”
He said that instead of turning to recordings of Thaw and attempting to impersonate the popular actor, he looked for inspiration elsewhere.
“I listened a lot to Michael Palin, who was from the north, went to Oxford and who was alive [in the 60s],” he said. “That’s how I imagine Morse’s voice to be.”
Mr Evans said that Scandinavian crime dramas such as The Killing and The Bridge had also left their mark on Endeavour.
He added: “There’s no denying that this character is a bit of a loner and slightly out of joint with his time and place.
“That’s what I find endearing about him. And perhaps the audience does, too.
“The world doesn’t need another detective series, so we have to do something different with it.”
Inspector Morse also inspired the spin-off ITV detective series Lewis, starring Kevin Whately, who played Chief Inspector Morse’s sidekick in the original detective drama.
Lewis was being filmed yesterday at Corpus Christi College and at Pembroke College on Monday.
Today, filming is expected to move to Broad Street and St Giles, with the crew expected to stay in the city until Saturday.
Producer Chris Burt said: “We feel wonderful to be back and Kevin Whately and Laurence Fox love being back – it is a great feeling.”
Mr Dexter has been given a cameo role – a long-standing tradition dating back to the Morse series — which was being filmed yesterday.
City councillor Colin Cook, executive member for city development, said: “I don’t see any reason why Endeavour can’t carry on for as long as the actors want to keep on making the episodes – this is fiction after all.”