I see no way anyone comes looking to trade for Couturier before he puts in a full healthy season (presuming he does). However, with the cap most likely going up a few million dollars next year, if he does prove he's back and healthy, I could see teams that strike out on the FA market looking into trading for him at 50% retention (we'll have that retention slot back from DeAngelo, at the very least), and on half his contract, he should be worth a haul.
At 100%, he can be a 1C on more teams than not for a couple years, and will very likely age gracefully into a high-level 2C for the back end of the deal, given that so little of his game is based on athleticism. Even in the worst case scenario, that's a $3.875M deal for Selke caliber defense at 3C for the remainder of his deal. (well, true worst case if you trade for him is LTIRetirement, but from an on-ice perspective.)
Obviously, all of this ends up modified by what we actually see on the ice this year, but we can only work with hypotheticals for now, and a hypothetically healthy Couturier is tremendous value on 50% retention.