As we wait for BlackBerry to issue a fix for this oversight, you will be pleased to hear that there is still a workaround to boot. The moment you launch BBM for iOS, do not press a contact name under Chats, but rather, a long tap on a contact name will reveal a slide out screen that appears from the right side. Located right at the bottom of the slide out screen would be a trash can icon that can be used to delete the whole thread involving the contact selected. Pressing this icon would bring up a new window, letting you “End Chat”. T
Once done, just head on to the Contacts tab, click on the name of the person whom you intend to “talk” with, and it should be all systems go then.