Its a pretty good theory, actually, since it has some pretty good evidence to back it up and as for me its not ridiculous, for Stan's memories did came back and Bill is in his mind so it may still be possible that Bill is still alive. Also, codat's theory makes sense too. We still don't know on what side axolotl is; Good or bad. If he's bad though he would've probably made the universe to be his slave already. Anyway, there is still no confirmation in anything related to axolotl.