Experiencing, having some notions about X is equivalent to "X exists", that is, x having specific ontological attributes
Since we cannot experience our death, our death does not exist
Take "suicide is painless, it brings so many changes" from M.a.sh
Yet we cannot in principle experience any of those assumed changes

So how would you explain experienced illusions? mistaken identities? etc.

Not every ecperience relates to an existing thing, but you are correct that it relates to attributes.