The obvious way around the problem of vanishing Jedi is to give it a better explanation in the PT.
I can't see why George could not have had Palpatine attempt to honour his deal with Anakin and use the Force to save Padme only to have it work in an unexpected way.
She becomes a ghost at the point of death.
Leia can see her as a girl.
Padme can show Ben and Yoda how to do it and appear in ROTJ at the end rescuing her husband.
Making Qui-Gon the key was daft, it solves nothing but having Padme the key maintains the continuity of the OT.