Of course how you 'destroy' daemons is another story as well - in one sense you can take away their sentience by breaking up the component 'elements' that make them (the same way a Chaos God is made up of invididual souls, daemons, etc. that reach a critical mass of consciousness.) but the entity does not actually go away - it just sort of goes into a hibernation or coma and periodically 'awakens'