Haiku Poem:
Current Yale Grad here.
Yesterday we got invites
To host new admits.
At April visits
For the prospective students
So, decisions soon?
I think you can take it that decisions are made and coming out soon. Yale does personal notifications from usually POI. Usually email. Some by phone.
Best of luck see some of you soon.
I don't think that there is an obligation to do this. School know that students will get multiple offers and turn some down. They are prepared with wait lists. It is probably good to turn them done as soon as you are sure though, at least for the sake of the wait-listers.