Losing Ellis and Pavelski isn't so bad since it looks like they aren't even keepers for you at this point, but what about Reinhart + Johansen? Who would become your last keeper if you were to replace those two with Marchand? Lee? JvR? Both are $7 million players, a considerable value downgrade from a guy like Reinhart I think.
So the deal basically becomes: Reinhart + Johansen for Marchand + Lee/JvR
I think the Marchand side is the better off in terms of raw production. Marchand is a 90+ point threat with his current deployment on a great team and should have high +/- as a nice complement. Lee or JvR are like 55-point guys who are both strong goal scorers signed for $7 million, so combined this side comes in at $13.125 million AAV.
Reinhart is probably a 60-point player with some additional upside as Buffalo continues to improve but his cap savings at $3.65 million only lasts for another season. Another strong performance and he is going to be in the $7m range with guys like Lee. Johansen also probably a 60-point player, hopefully the Nashville PP can improve a little bit to help that outcome. At $8 million, he's not really a great contract in your setup with goal-heavy scoring.
I think it seems a little expensive, but you get the far better keeper group at a cost-controlled, reasonable price point ($13.25 million for the next 6 seasons vs. $11.65 million for 1 more season). Marchand is easily the best player in this whole trade, and you should acquire him. He's an elite keeper on a great value contract for long-term, and the cost is two mediocre keepers (one of which you can easily replace w/ Lee or JvR) and a couple extras who weren't even going to make the cut as keepers. This is a slam dunk for you.
Keepers: Schenn, Strome, Marchand, Giroux, Labanc, Atkinson, Arvidsson, Lee, Josi, Rask