I think if Gibson commits, Gentry would definitely sign elsewhere. If Gentry commits, however, I think Gibson may still commit to us after his senior season. Gibson's an elite (top-10) prospect and - even with Gentry around - he would still have a better chance for immediate playing time at Tennessee than at Auburn or Ohio State.
In fact, Gentry may know there's a risk that Gibson could still commit to us after he does, so perhaps that might deter him from committing to us in the first place. If Gentry and his family have been doing their homework, they would know all of the things Gibson says UT has been telling him (e.g., that UT refrained from signing a QB in 2014 specifically to get him, that he's
"the only quarterback [Bajakian] recruits until [Gibson] tells him otherwise," etc.).
I'll be ecstatic with either guy, but we could very well get both if Gentry commits first.