If i leave books out in the megaton apartment, not in containers- do they disapear?

No, as far as I know.

K,thanks.

The only time dropped items should ever disappear is if NPCs pick them up. The only times that should happen are when they are entering combat, and I believe that they will only pick up weapons and ammo should that occur (and only if there is ammo for the weapon).

Cool that they can pick up weapons to fight with.