Sens fans are still in the denial/reasoning stages of grief here. The only player with NO leverage of any sort in this situation is Pierre Dorian.
Yes, we all agree that Karlsson with an extension should be worth a blue-chip prospect. However, there is zero chance that any teams are offering a blue-chip prospect, and Karlsson holds all the cards in his hand, even if he does want to sign an extension with Dallas or Tampa. Would Karlsson rather play on a team WITH Sergachev or Heiskanen, or without? That's a simple one to answer, and Karlsson can ensure that happens by refusing to discuss a contract extension prior to the trade.
On the other hand, Sens fans are committing to a major fallacy by stating that they can hold the player until the TDL. What does that accomplish? An attempt to spite the Avs by finishing slightly higher in the standings? One errant skate to the back of of the heel over the first 50 games, and you get nothing in return for a valuable trade asset. You can push this out another couple of months, but the organization gains little and risks everything by having Karlsson on the roster on opening night.