Once the player has cleared the building of raiders (and the ones who come in after the initial slaughter), no enemies will respawn within the interior. Also, stored items do not disappear from containers.
In the Bethesda demo videos of Fallout 3, a character called "Dead Mercenary" appeared outside the store. This character does not appear in the main game, even as a random encounter. The Dead Mercenary was equipped with Combat Armor, a Bandana, Biker Goggles and a Chinese Assault Rifle. The character bears a close resemblance to Sydney.
