Added more death deets to the FAQ that should answer most of your questions.

As for knowing what they lost, it depends! Do whatever makes the most sense for the memory you're choosing. It won't be "I no longer know this" no matter what, and instead: "I tried to access this memory and no longer have it". Like trying to remember someone, and the memory slipping away, or trying to do something you know you're good at, and suddenly being terrible at it.