Hey there,
For this, you basically need to create a boolean variable and a condition (branch/if) before destroying your actor or hidding it. Yoru condition is, did this character talked to me?
Once you talk to this character, you cast to your actor blueprint, get the boolean you are using for this condition you’ve just created, and set it to true.
Then, back in your actor’s blueprint or you level blueprint depending on how you are doing things, you do the destroying logic.