When you ignore a narcissist do they instantly forget kind of like out sight mind?

No, ignoring a narcissist typically does not have the effect of making them forget. Narcissists can have poor emotional regulation and a strong need for attention, so being ignored can increase their focus on you rather than cause them to quickly forget. Moreover, they may actively try to regain your attention and control of the dynamic between you two. To deal with a narcissist, it's better to seek guidance from mental health professionals experienced in handling relationships with people like this.