I keep watching Navy on this. Look at them after Kaipo graduated. Were they as proficient on O with him gone? No. Did they find a QB after Kaipo who could run the O and did the O production suffer greatly? Yes and no. It'll be the same next year with Reynolds gone.
I don't think there's any reason to think that we won't do the same when JT graduates. We won't be as hot with him gone, but either MJ (probably) or someone else (maybe) will step in and run the O at just about the same level of efficiency. If it's MJ, look for Byerly, part dieux; I think their level of talent is very similar, though Tim could throw better. In short, I'm a lot more worried about finding a reliable BB for next year then I am about finding a QB in 2017.