For what it’s worth, I still think the notification should be deleted/cleared if the recipient is no longer able to view the message. Having a backstop (the “Dismiss” button) is good, but it’s still a bit like gaslighting the user that the notification sticks around. In addition, the button dismisses everything, which might not be what a user wants. (Though, in fairness, most people will only notice the problem if they’ve cleared all their other notifications the normal way.)