It wouldn't surprise me if Staios looked to trade Chabot for a cheaper alternative, but I think Sanderson emerging as an excellent powerplay QB (2nd in the league in PP points for a reason) should probably kill the idea of Karlsson returning to Ottawa.
Pittsburgh had the option to go full rebuild at this year's deadline with the crazy prices being paid for talent, but they chose to hold onto guys like Rakell, Rust and Karlsson. They apparently aren't willing to blow up the team while Crosby, Malkin and Letang are still on the team, and given the decline of Letang, I don't see them giving away Karlsson for nothing to get his contract off the books.
I don't think it makes sense to trade much for Karlsson if he's only going to QB our 2nd PP or push Sanderson out of a role he's excelling in. Have to think we'd get outbid at the very least by teams that actually need a offensive D of his caliber.