Marvin Humes described Cowell as "the best judge in the world", prompting his bandmate and Got To Dance panelist Aston Merrygold to quip "second-best judge in the world!"
"He has to return, definitely," Humes told Digital Spy and other journalists this week about Cowell's possible comeback to the UK show.
"He still does Britain's Got Talent. Obviously with the schedule of the US X Factor it's very difficult, but he has to come back."
Asked if The X Factor had lost its power to break new artists, Jonathan 'JB' Gill said: "I don't think so. Obviously you can never tell.
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"You have to wait and see what happens to the next batch of finalists, or people from the show next year. See who's doing well and who's releasing.
"I don't think it's on the way out at all. People say, 'The winners never do this, the winners never do that'. But there are winners who have been successful - and it's not just down to the winners."
Gill continued: "It's a competition, yes, but it's also a way for people to get into the industry - whether you win, or whether you come fifth, or last in the competition.
"You've still achieved something and there's still the scope to do different things. Look at Ray [Quinn] - who came second to Leona [Lewis, in 2006].
"He didn't necessarily release an album, but he did loads of musicals and was in the West End and things like that.
"He's not a proven international smash artist or whatever, but he's been a success in terms of career in the entertainment industry.
"I don't think that's going to change. As long as X Factor is running on TV, we'll definitely have success stories from it. "
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Oritsé Williams added: "The show definitely has legs, as long as people enjoy it and want to watch it.
"It's still the most talked-about show on television. It still gives people the opportunity to expose to their talent in ways they wouldn't have had otherwise.
"It's the most auditioned-for competition in the world. and it's the most anticipated television programme of the year."
JLS feature on seasonal special A Very JLS Christmas on Sky 1 HD next month. Their new single 'Give Me Life' is released on December 23.
Photo gallery - 'X Factor' shock exits