He is going to regret declining that
I'd be very surprised if he didn't end up getting an offer in the same ballpark this offseason. He's a guy who has shown the ability to play against the opposing teams best players and still produce 45 points a season. Over the last 5 seasons, he has 187 points in 333 games which is a 45 point pace over that time while playing against tough competition. A team will take that bet and these type of players typically get paid and provide enough value to make it work.
Over the last 5 seasons Pageau has produced at a 37 points per game pace while having a similar role and he did get paid for that even though he's had really good seasons and then some very average ones. I think Danault has had better linemates overall which has resulted in a better point production but I am expecting a very similar contract to Pageau with Danault.
He's had a tough year but he's clearly an asset. GMs see the value in this type of player. If I had to take a guess I think he's getting something in the 4 years and 5M range.
I also think there's a unique opportunity for him being a free agent with the expansion draft. Seattle will definitely be stealing a couple guys from teams and these teams will then be looking at the free agent market to replace their lost player. Seattle will also likely look to add UFAs so these are all additional options for Danault in a market where there just won't be a lot of centers available in free agency. Krejci, Stastny, Zajac, Bozak, Getzlaf, Staal are all 35 or older. If a team is looking for a medium to longer term solution it pretty much just leaves Danault and Granlund who have somewhat of a track record to show.