I hope they don't have to retain on Mantha, Edmundson, or Pacioretty to move them. All of them should be affordable enough when prorated at this portion of the season, and on expiring deals. Unless retention knocks their value up to something silly (like a 1st round pick), I think there's better use of the retention slots.
Dowd should be one of them, given that retaining on the remaining year of his deal has the potential to significantly drive up his value to contenders near the salary cap.
Beyond that, they have potential to actually utilize their remaining salary cap space to accrue additional assets by playing the middle men to other teams trying to maneuver their cap space. Arizona picked up a 3rd for facilitating the Patrick Kane trade to New York. Minnesota picked up a 4th and a 5th between the Orlov and O'Reilly deals. These aren't game changing assets, but it can essentially be "free" picks to add to cupboard that don't hurt Ovie's goal chase in any way. And I'm skeptical that retaining on their UFA rentals would be worth much more.