For some reason I wouldn't be surprised if Yuko's still alive and flickin her bean watching from a crack in the closet door like when she made Gen hide with her while Reiji's dad beat his ass.
If she's actually dead, I'll be surprised, her whole character was given the role of being this undying, unkillable demon woman that haunts the entire town and destroys the lives of people who get close to her.
If she suddenly dies now because Gen killed her, then getting stabbed with Reiji (idr if Yuko got stabbed too or if it was just Reiji though lol) and then getting hit by the teacher's car didn't kill her, then dying cause Gen killed her for helping him accept and come to terms with his identity would be dumb. Even if she talk-no-jutsu'd Gen's dad into hanging himself lol