User blog comment:Touchinos/Supernatural Season 15: Endgame/@comment-1031724-20190323233642/@comment-1031724-20190324224235

Because, they're obviously setting Lucifer up to be revived, and while Jack's powerful again after absorbing Michael's grace, Lucifer still has the grace he took from Jack even in death (presumably why a human could awaken him in the Empty), and Jack can revive angels (or at least awaken them in the Empty so they can annoy Cosmic Entity into reviving them), so he'd probably revive Azazel as well, if nothing else then to annoy Sam and Dean, coz he's their archnemesis.

I'm sure Jack could kill him, he not only empowered Castiel to kill Dagon but also killed an archangel. Though if he goes evil from lack of soul and has to be sealed away, he might not be around to do so by the time Lucifer returns.