Explain why Empire Strikes Back doesn't come out and say Leia is Luke's sister then. They dropped hints leading up to that, but using your theory then they would have said so at the end of ESB otherwise that's "proof".
Sure no one dies like Kreia did, but the point is a story string was still left hanging despite clues being dropped about it, and despite the fact it was never resolved at the end of the movie.
If KOTOR2 is just the middle game in the series (like many suspect), then everything doesn't need to be wrapped up at the end, despite the death of the character. Handmaiden could just find out later about it after Kreia's death.
I don't personally think Kreia is, but your "proof" is weak at best.