Ultimately, the duration will depend on JG's behavior. If he continues womanizing and getting caught, he may never be invited back. If he 'confesses his sins' and pays his penance, eventually it'll fall into the rearview mirror. Last I recall, he was denying that any of the accusations were true, so I don't think the clock has started for him yet. Then again, he's pretty much completely disappeared from view, so that could serve the same purpose.
If he stays quiet and under the radar, I think it could be in the range of 7-10 years before he starts reappearing. My guess would be that it will initially be low-key - he "shows up" at a golf tournament or one of the recruiting re-cap events. Not as an official or announced attraction, but as a sort of 'oh, look who's here..." If he's not booed out of the room, maybe he actually gets invited to the next one. It'll build based on how people react...and the impact it has on donations.
Problem is that another 10 years means at least 3 more QBs move through the system, and his star will gradually fade. Even before the scandal, he was probably only #3 or 4 on the list of QBs people wanted to meet (behind Bledsoe, Leaf, and maybe Thompson). Now he'd be passed up by Minshew for sure, probably Falk, maybe even Kegel.
I look forward to when they start bringing Minshew around to events. I'm not a golfer, but I'd pay the price of admission and a couple overpriced beers to hang around with him for a couple hours, and I know I'm not alone. I suspect that the price of admission goes up if he's in attendance, without putting much damper on demand.