If it came to trading him the Kings are 100% taking a lesser cap dump along with a few nice pieces for Carter.
A few nice pieces sounds like a lot. A 26 year old Carter brought back a few nice pieces. A 27 year old Carter brought back one nice piece, and at best a decent player. A soon to be 34 year old Carter, coming off an injury to his leg, which may or may not hinder him in some way, on a team that may or may not continue to struggle as the season plays out, I think other GM's would pressure Blake. Looking at what Lombardi traded to get him, when it was clear Carter wanted out of Columbus, it wasn't the largest price to pay. Plus Lombardi was desperate at the time. His job may have been on the line if the Kings don't make the playoffs that year. A lot of different variables there.
My expectations for a return on Carter are the equivalent of what they traded to get him. I think that's the best they could realistically do right now. If we're talking a contender, that's probably a 20-31 pick, and a guy off the roster to make the cap work. Multiple nice pieces for a 34 year old Carter with 3 more years left after this one? That sounds like a lot. Looking at the few bigger trades around the league over the last few years, not many of them involve that old of a player, with that much term left, bringing back a ton.
While Carter's contract does back dive a bit, it's not the same as Hossa or Zetterberg. His contract ends when he's 37, not begins back diving when he's 37. Teams will probably have to account for the $5m cap hit through 2022(assuming no lockout), which makes things more complicated, because cap space/flexibility is so damn important. Plus so many younger players are now getting the giant contracts earlier. That only makes future cap space that much more important.