Pageau is going to be traded. No way we pay him 4M+ over multiple seasons on an extension. If he was not hurt this season, I think he would have been dealt in the 2019 off season at the latest, but now that he'll miss so much time, maybe we have to keep him until the 2020 TDL to properly showcase him and rehab his value.
Including this season, Tierney has 3 years of team control. I could see him being in the same boat as Pageau, just one year later.
The only way we keep either is of they cement themselves as legit top 6 players. I think we'd rather pay a true 2C 5M+ than pay a top level 3C/middle 6 type Bonino/Hanzal money. Pageau is a warrior, so we'll get a good return for him at the 2020 trade deadline so long as his injury hasn't ruined him.
If Duchene leaves, it increases the odds of us keeping either or both of Pageau or Tierney.
If we actually intend to sign Duchene, I think we're looking at Duchene as the 1C, White in the former Pageau role as the heavy lifting 3C, and Tierney in the 2C role (even if he's not a 2C) until a prospect like Brown or Chlapik breaks out (not a given).