Because the advantage is good when someone is voted out at final 4 and they have the advantage they are automatically returning for the next season
Where did you hear that?
Sorry, but this is false information.
And suppose Ken goes? Does he also pass it on or does it die out?
I've been thinking about this as well, and I'm unsure actually. I suppose he should have to pass it on, as I don't think the producers would risk introducing a new twist/advantage with a possibility for it not to be revealed at all.
With that logic, Jessica could theoretically been voted out in the premiere with the next holder of the legacy advantage gone the following tribal. And boom, then the advantage is gone for good? Doesn't seem sensible.