I think any chance of a happy ending went bang-bang. Raputa-chan crossed a line she can't cross back over, so I expect one of three things to happen.
(1) Nightmare ending. She takes over Kei too and forces him to love her/enslaves him.
(2) MAD ending. Her and Kei both die.
(3) Humanity ending. Her love for Kei manages to shift out of Yandere-mode and she self-destructs herself along with her creator, he ends up with the girl in his class.