Stop Notifications from Disappearing After a Few Hours

[Richard Feynman]

Unless I am wrong notifications just disappear after a period of time. As an example I received a text message earlier today about a business matter and I purposely didn't open it because i wanted the notification to server as a reminder later to address the issue. But now the notification has disappeared.

I don't see any settings under Notifications for adjusting this. Does anyone know:
A. How long notifications stay active?
B. Is there any way to change the setting (or apps to do so)?

Thanks