The only argument I can see against keeping Stone is that he'll make us too good to tank our way to 4th overall or better next year....but I think this season might be proof that we don't have to worry about that in the short term.
Even if the offer is something like Roslovic, Niku, 1st, conditional 1st, which we've been told by other fan bases we'd be crazy to get, none of those pieces are likely to progress into anything close to the best winger in the league who'll still be in his prime when our supposed window hits two years from now.
With the way Stone has played the last two seasons, he's as valuable as a 1C of Duchene's calibre. He drives his own line with an inferior C. Look at how effective his line has been with Tkachuk and White on it. Nothing against either Tkachuk and White, they will be legit 1st or 2nd line stars in this league, but they are 3rd liners on most decent teams, and Stone has transformed them into 2/3rds of by far our most effective line.
Zack Smith's great great grandchildren will be visiting Mark Stone in his retirement home, thanking him for buying them houses via letting Smith play on his line in 2017.