I can see how Krang being killed would work for the narrative, but then again, there's the other "erasing potential" situation in not killing major characters. And in some ways, there could be use for him. But then again, he's the only character "major" enough that could potentially go down. And even then, Shredder will be returning for sure, or at least just his re-animated body. (Ew)
Plus, it would add fire to the Ch'rell storyline when that finally comes along. Vengeance for a death would be far more dramatic than vengeance for imprisonment.
Though, from the way he's been used as a "major" character for this particular set, it could very well be Hakk-R and I'm just chasing a red herring
. He probably won't have much of a place outside the story he's in, much like Darius Dunn.
But Krang is more likely. At least Donatello seems to be involved in one last fight with him, since he wasn't involved in the other two.
I can see him having a cathartic death. Maybe attempting to take down Maligna and having enough of an honorable death that he could be put to rest on Burnow Island.