The worst case scenario might be CBJ missing the playoffs this year and not winning the lottery.
Duchene walks because he wants to go to a contender, meaning no 2020 pick for us.
The pick probably ends up in the same range as it would had they made the playoffs and not made it to the conference final.
The best case scenario might be CBJ missing and winning the lottery this season. Especially if they can do a sign/trade with FLA to send them Panrovsky on an 8 year term and get back someone Duchene has chemistry with like Hoffman. So all of a sudden they can go to Duchene and say look we missed this year, but we have Hoffman, Dzingel, you, and we also have Hughes or Kakko on their ELC. Duchene signs, we get their 2020 and 2021 picks (presumably unprotected) and with Bob/Panarin out, even with those additions, they probably aren't a lock to be a playoff team going forward and we have basically their entire top draft picks for two seasons straight.