Hey, you know, that's a good question. One thing WE as DUNE readers fail to remember some times is that the Bene Gesserit Order changes and evolves... and so does their abilities.
I'm willing to believe that the Reverend Mothers (and the rogues ones too) in the first 2 or 3 Dune books could only pass on their "memories" upon their death (perhapse passing on the memories would bring about their death... who knows?). However, what's to stop the BG from evolving too? One thing we do know is that by the time Chapterhouse came along death and sharing were no longer intrinsic to the other. This, I believe, is closer to the truth. Along with everything else in the Old Imperium, the Bene Gesserit also evolve.
IDAHO, You've got a great question...