Just got this response today so just an FYI for everyone.
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Thanks for the question. The Deathtrooper die is not tied into Krennic after his ability rolls it in, so you cannot use Imperial Discipline to turn it. If Krennic dies, the Deathtrooper dies stays in the pool until it is resolved or removed. The original ability created a lasting effect that is still active. The Deathtrooper die is still a character die for the purposes of other effects, though.
May the Force be with you,