They certainly would've had the opportunity to keep Barnabas mortal if the show had continued, what with Angelique lifting his curse during 1840. Obviously there are questionable timeline issues there, but DS always ignored those anyway.
I rather liked non-vamp Barnabas during the 68 storyline. Though, it would have gotten old to have repeated attempts or threats at turning him back into a vampire, or to have evil characters hold it over his head to manipulate him, as with the Leviathans.
I wasn't alive when the series originally aired and thusly did not watch it until 30 years later. But I would imagine that for the rabid fanbase of kids/teenagers who were watching, they probably would not want to see non-vamp Barnabas for long stretches of time. Hell, I doubt many fans now would want to see that. But there is a lot of story potential there and I wouldn't mind.