Z most definitely has major incentive to come back ASAP and prove he's the same dude he was before the surgery. At almost 30, back injuries with surgery would scare most teams including GB.
I also wonder if he was told in summer he needed surgery, he refused, tried playing with it and now here we are. In some ways that might have pissed off the Packers because if that is the case, he could have had it and already been back and playing.
Even if he returns to form, I do not see GB extending him. At least not the contract he wants. I think Gary is really developing into what they envisioned and they'll spend a 1st/2nd round pick on a pass rusher. Cheaper, younger option with much more upside.