Being that it's only guaranteed for injury, the Pats can pick it up and cut him if he doesn't work out and it costs them nothing.
That's still a fairly significant risk, though. Players get injured a lot, and that's ignoring that Cooper in particular seems as susceptible to them as anyone, and perhaps more than most.
The way I look at the fifth-year option is that there's one question you need to ask first and foremost: is there any realistic chance that the player in question ends up being worth what the fifth-year option costs? Typically, the answer is yes. It certainly has been in the cases of all of our first rounders, partly because they're cheaper as 11-32 picks and partly because the Pats draft well.
But with Cooper, even in the best-case scenario, I don't see any way he's worth taking a $12M cap hit for next year. So what's the upside? At best, it maybe grants you some leverage in negotiating a long-term extension, but if everyone in the room knows you'll never actually pay the guy to play for that amount, then you don't get any of that either. Picking up Cooper's option entails a fair amount of risk in the event that he gets injured, all to protect your right to pay a player $12M next year when you pretty much know for a fact you wouldn't even
want him for $12M per year. No matter how I look at it, there's nothing in it for the Pats.
I would be shocked if they pick up his option. Much better, IMO, to look at this as a deal for one year of a starter-caliber guard in Cooper. If he plays decently, maybe they resign him at a reasonable price that's a fraction of his fifth-year option. If he's so good that someone else is willing to pay him anything close to $12M per year next offseason, we let him walk and take the compensatory pick.