Board Thread:Questions and Answers/@comment-24728184-20140313185356/@comment-251103-20150813074127

I think the Rat King is technically undead, and he could return. Perhaps, as in the eighties series, he makes the acquaintence of Shredder, who quickly realizes he's too mentally unstable to work with. Also, Karai is still out there, and hungry, which would probably make Rat King and his giant pet rats very nervous.