every b-school follows a different process and its hard to tell what they will do - send a reject letter or feel rejected themselves

You should go ahead and withdraw your application and inform the b-school you plan to attend. As per my understanding they should accept what you tell them, as the rejection letter may only come later in the day when they release decisions for all other applicants.
It may suffice to send the admit b-school a copy of the email where you bid goodbye to the interview b-school. But, you should do that only if they ask for it, not proactively.
SatrioGenteng
Thanks for your reply!
Just to confirm — if I
withdraw my application by email, will that still result in a
formal rejection letter being sent automatically (or during decision date)?
I’m in a situation where I really need the rejection letter for admin reasons, so I want to be sure. Have you (or anyone you know) seen a case like that where a withdrawn app still got an official “rejected” email? Just trying to be extra certain 🙏
MBADecoder
I think you will receive a rejection letter eventually.
You could possibly tell the b-school where you are admitted that you withdrew your application to the