Not sure if true, but I read he declined an offer from PSG. Could also be that if he leaves he wants Valencia to get something for it, especially considering their economy isn't the best.
I can understand that as PSG have Nuno Mendes as a longterm starter so Gaya knew he wouldn't get as much playing time as he wants there. I guess he thought he wouldn't be a guaranteed starter here for next two seasons as well with Alba ahead of him but things have changed now.
Anyway, while I'd like to get Gaya (especially for cheap/free) he's also not a can't miss player especially not now with Balde's breakthrough. Would still like for both Alba and Alonso to leave next summer and bring someone to compete with Balde. World class LBs are extremely rare these days, signing another U23 talent (unless they believe he can turn into a close to a WC quality player but have no idea who that could be) also makes little sense in this situation so I'd be ok getting a proven La Liga player like Galan for example. Or maybe sign a hybrid LB/LCB (if we'll use 3-4-3 more often) like Hincapie.
Our focus should be more on finding a good RB though. Probably need to sign two new RBs but with our past experience even one will be hard to get.