Before CE decided to leave, I read in quite a few different places that the original ending involved The Doctor and Rose in the console room.
The Doctor had absorbed all the time-energy from Rose (as before). He then told her he has taught her all she needs to know, and then opened the TARDIS doors and leaped into the time vortex (I assume because he thought he was going to explode or something).
And that was going to be the season cliff hanger - Rose alone in the TARDIS and The Doctor flying through the time vortex.
They changed it to the regeneration scene once CE announced he was going and had to re-shoot. As far as I am aware, the only scene they re-shot was the final scene in the console room, so everything leading up to that was exactly the same.
That's what I read anyway.