Okay… but from what we know about regular essence transfer it’s made quite clear that there are only 2 options:
- Possess the person that killed you
- Or die forever
That is why I’ll always advocate for the Plagueis theory. That he learned a secret that allows him to premeditatedly prepare to expel his own spirit at any point. Again, I have to mention that the novelization makes it clear he somehow possessed a clone before his original body was even killed.