Simply put, the Oilers will not have the cap space to even offer Jake Guentzel a contract extension - unless they move out a core player which is extremely unlikely. Dubas has done Guentzel a favour by giving him the ability to talk to other teams an negotiate an extension elsewhere, but it will hurt his standing as a pure rental player.
Guentzel would've been the best addition possible for the Oilers this deadline as an offensive threat. The 29 year old forward is a proven consistent scorer, and is having a great year with 22 goals and 52 points in 50 games.