Even if he takes less this upcoming season on a new contract. He would have guaranteed money for years. He's gona sell himself as healthy if not close to healthy he's probably not looking for the Max but for a good contract for the next 3-5 years On the other hand If he opts in and gets injured or shows his injuries continue to be a problem his stock might drop significantly. If I were him I would sell my self as healthy to the best bidder and lock that money up as soon as possible!
He has to opt out(or in) before free agency. He doesn't get to enter free agency... "Oh damn, well no teams want me so I'll opt in."
Right , but his agent should and will put out feelers to determine a market for him . It may not be 100% accurate , but Dwight's team should know about how much he would get paid .