In the grand scheme of things, I doubt it. I'm sure there'd be some degree of nostalgia, at least initially, upon a return of Jeff Jarrett. Aside from that, I don't really see Jarrett contributing all that much.
After all, Jarrett was a central figure in TNA for years and, just me personally, never did much of anything for me. I've always been someone that's never really seen Jeff Jarrett as a headliner, at least not someone who is a constant presence in the main event scene. As a mid-carder or tag team wrestler, I thought that he was just fine and pretty damn solid overall.
If the reports are true that Jarrett has, for all intents & purposes, been ousted from TNA, then it sucks. As a human being and a wrestling fan, I respect Jarrett for going out and doing his own thing with TNA. That being said, Jarrett turns 46 years old in about 3 weeks, so he's not the future of TNA. Bringing him back would ultimately lead to another aging veteran as a central figure in a major storyline. With Sting, Angle, Hogan and Bully Ray as, easily, the top guys on the roster; adding Jarrett to that mix won't improve things.
If TNA brought Jarrett back and he was used to ultimately put over younger guys, someone like Magnus for instance, then I'd be fine with it. It probably wouldn't lead to any increase in viewership or anything, but it'd be a sign, to me at least, that maybe TNA could get firmly behind Magnus as someone that's a top player in the long run. If they wanted Jarrett as a mid-card wrestler or part of a tag team, I'd be fine with that as well. Jeff Jarrett can still be useful, just not as a main eventer.