There is no question in my mind that Padme will die in EpIII. GL would never leave a major characters future untold and unfinished, and i don't think this extra scene they have filmed for ROTJ would explain her death anyway because it is said that the new scene will be placed when Leia is talking to Luke about her mother and how much she remembers her, so showing Padme dieing when Leia is reminiscing just wouldn't fit right. If Padme is killed of in EPIII(more than certain she is) i think that it will be relevant to when Anakin finally crosses to the darkside - its definitely something that would push him over the edge.
As to the continuity, your guess is as good as mine. But she will not survive.
The case rests.
There is NO new scene for ROTJ!
And it is not SO unlikely that GL will not finish her tale. And it is very awkward plot-wise if she dies before he falls. It is so inconvenient to have the twins and squeezing in Ob-Wan fights an so on for an event you would really think is the end of it.
And we can NOT just ignore the continuity issue!
It's POSSIBLE, yes, but I don't see why that is any better position than saying she does not die in the film. I believe there are serious problems with both points of view so far and to be so certain one way or another is a mistake.
As I said... it is thematically appropriate (though that does NOT mean essential), but difficult plot-wise.
Again, this is a rather extended rationale for something FAR more simply explained by saying that Leia was with Padme for a significant amount of trime on Alderan.
This is sci-fi and with extended rationales you can explain ANYTHING but the simplest situation still has the best call for the truth.
I think a few hours is not sufficient to explain Leia's ROTJ line, anyway.