With Zaitsev not playing in the NHL anymore, I wouldn't be surprised if he went back to Russia and simply voided the last year of his contract with the Sens. Worst case, we ship him elsewhere for a 2nd when he has 1yr left. It's not a big deal.
Zaitsev isn't going to bail on the roughly $6 million he is owed.
I wonder if the Sens can make a deal with a KHL team. Say they want to pay Zaitsev $500K for the rest of this season and $1 mil for next season. They loan him, the Sens pay $4.5 mil and the KHL team pays $1.5 mil of what's owed on the contract. This is what happens when a coach is fired, and gets a new coaching gig before the owed contract is up.
Another option is wait until he is paid his $2 million bonus July 1. Then trade him to a team like Arizona with his $4.5 mil cap hit and $2.5 mil cash owing. What would the Sens have to attach? A 3rd round pick? It helps Arizona save money, as they can go another $2 million below the cap in cash paid out.
As for Karlsson, I'm sure the potential new owners of the Sens would love more star power on the team. The difficulty is the money retained. The Sens won't want to pay $11.5 mil for another 4 years. The Sharks will want a team to pay as much of that is possible. Where is the sweet spot? And as the retained money goes up, the asset cost to acquire Karlsson goes up. Karlsson at $11.5 mil might be worth a 4th round pick. Karlsson at $8 mil might be worth 2 1st round picks. (note: I'm just making this up, I have no idea how much Karlsson is worth in trade at these 2 salary levels).
If Karlsson is acquired, the Sens will need to trade DeBrincat, as Karlsson is getting his future money. I would do that, as great as DeBrincat is, the Sens have lots of high scoring forwards, and basically has 3 solid NHL defenseman.