You're conflating several different things. Removing yourself doesn't stop "existence" as a concept, but nothing would. It would stop your existence, but that's not what you said. "Existence" as an abstract concept, doesn't have meaning because you're applying a metaphysical concept to basic material truth.

It's as silly as asking if there is a purpose for this rock. But that's not what anyone's talking about, and that rock doesn't have agency.

We are talking about your existence, a person with agency and competence.

There is nothing narcissistic about deciding your own purpose in life. In fact, it's the act of a mature adult who's taking responsibility for his own life.