You at least get 3 years of MacKinnon at ~3.75m. With Duchene set to make 7+ and ROR 6+, that stays in the 16-17m range. Whereas Stastny staying puts all 3 staying around 19-20m. It can be done either way, MacKinnon just gives a bit more headroom for 14-15 and 15-16.
As for wings (assuming Downie is re-signed) we would have Landy, PAP, Downie, McGinn, and Jones in the NHL. Sgarbossa could possibly play LW in a couple years, and maybe the prospect demanded in a Stastny trade is a winger or the pick is used on a winger like Mantha. Or sign Stalberg this summer with the freed up money. There are options to fill out the top 9.
Just a thought.
Duchene is not a UFA, hes not getting 7+ while hes got RFA years left. Everyone thinks that RFA status does not mean anything after what O'Reilly did, but that's far from the truth. How many players are going to want to go through the same thing he did? Duchene also said specifically that he wouldn't go about things the same way O'Reilly did.
I also don't think Stastny is going to net the kind of return 'some' people are hoping for. Basically enough to make it worth more to trade him than keep him. At least without adding some sort of strong piece going along with him like one of Barrie, Elliott, or Sgarbossa.
There will not be a ton of teams looking to add 6M in salary, if we have to trade Stastny I have a feeling it's going to be disappointing. (Which is why those scenarios are not as much fun to think about for me.)
Edit: I also hate even thinking about the idea of relying in anyway on David the ghost of pirates past Jones, for any sort of production. Which means in any way counting on him to be a regular top 9/6 forward on a team that roles three scoring lines.