The storyline in the original Final Fantasy Series had little or nothing to do with Kingdom hearts, this too apply to the characters....

So if Vivi stopped in FF IX, he can still be alive in Kingdom Hearts just like Sephiroth....

But if you mean Ursula and such....well, I dun really know. Did Ursula died in Kingdom Hearts 1 is still a mystery since a screenshot of her in Kingdom Hearts 2 is shown....