Nelson turns 33 next October - if you move him for futures - you get cap space and prospects.
Essentially, Lou could
Trade Nelson, Mayfield, and Varlamov for futures and picks. And use that $ for top 6 winger in free agency and get younger.
Take the Mayfield $ (Mayfield turns 31 next season) and pay Gavrikov, who turns 28.
Horvat and Barzal play C and take Nelson $ and sign of trade for a F making a similar amount, like Bertuzzi or Boeser. OR Isles can take the assets and flip them for DeBrincat or Meier (if he isn’t moved by the TDL).
Sign a back up goalie who can play 20 games a season, while Sorokin give you 55-60 starts.
I don't like this at all.
1) Nelson has arguably been our best forward at a sweetheart deal. 6 mil for him has turned into a bargain. He also has 2 years left on his deal. Imagine getting a 30 goal scoring center, at age 32 for 2 years at 6 mil? I'd sign up in a heartbeat. If you're rebuilding, he'll bring you back a ton. But you don't trade him just to sign a guy for too much money on too much term. Also, aside from Pasta, who would you prefer to allocate the 6 mil for? Besides, Pasta is likely return to Boston at close to the max.
2) Gavrikov is not good and will get overpaid. His best asset is playing a lot of minutes against tough competition, and he doesn't do particularly well in those situations. He's on a bad team, so he's probably better than awful. However, he will get overpaid. I want nothing to do with Gavrikov.
3) I like your idea about Meier and Debrincat. However, they will both cost more than the 6 mil for Nelson, with Debrincat not bringing as much value as Nelson, and at a higher cost. Meier, on the other hand, is an elite power forward. But will cost around 9-10 mil (3-4 mil more than Nelson). Boeser is a huge downgrade from the other players mentioned, including Nelson. So getting Boeser while losing Nelson is a horrible move - at a higher cost, no less.
If Isles choose to start rebuilding, Nelson is a great place to start though.