No bells, no whistles, no notifications -- WhatsApp lets you leave the messaging party without so much as a peep (and only a whisper to the chat admins). The process is easy, and gives you a one-way ...
You can only leave an iMessage or RCS group chat in the Messages app if there are three other participants in it. If you're in an SMS/MMS group, you can either mute it or delete and block the thread ...