Ottawa is in a weird spot because its pretty likely that there unprotected 1st will belong to Colorado next year. Which means the team isn't going to tank next year as they would get nothing out of it. I think they try to turn things around with a new coach next year.
I think Hoffman is gone this deadline or at the draft to give cap space to a Stone extension. They should get a 1st, prospect, and roster player as compensation.
If they are out of it half way through the 2018/19 season and they are out of it they have no choice but to start trading off expiring contracts.
Duchene, Brassard, and Karlsson will all be traded away unless they want to sign an extension (which is doubtful if they spend two years at the bottom of the league). Best case scenario is to let teams talk to the players and work out an extension it would increase there value.
I don't think they'd have to rebuild for to long honestly. They have White, Brown, Chlapik, and Batherson who could end up being impact forwards in the NHL. Stone, Ryan, Smith, and Pageau will likely be kept around.
Chabot on the backend has loads of potential. Hopefully there first this year will be used on a defenceman. Phaneuf, Ceci, and Claesson kept around until prospects take there spots.
And if you include the returns from Hoffman, Karlsson, Brassard, and Duchene (all will bring good returns) Ottawa will have an overflow of youth.