So, I got accepted to 8 universities and after I choose which one I will attend, do I have to notify the other 7 schools that I will not be attending there?
It’s a professional gesture. A simple email will do.
Some schools send a card to reply with. If not an email is fine. You don’t have to (they will figure it out when you don’t send a deposit) but it is absolutely the right thing to do.
I would do it so another person could come off the wait list that much faster if possible.