Honestly, I don't see the Sharks retaining on Karlsson. It's not just the dead cap, it's also the years of it when they already have retention on Burns.
With Burns, this would tie up 2 of the 3 permitted retention slots for years. 4 for more for Karlsson and 2 more for Burns after this season. For a rebuilding team, having only 1 retention slot left is huge. It handicaps their ability to be a trade facilitator for years. It would require a sizable haul to do that in my estimation.
this trade is not that haul.