Tested with default prompt and adding things like - Do not end call without saying yada yada and a bunch of variations of this.
If I call in and just say Goodbye after the initial greeting, i get an immediate end-call reguardless of what i've tried to put in the prompt. In other instances we have it follow a after hours message intake for example and then if you have it confirm... Is there anything else I can do for you and you say... No. thanks that's all... abrubt drop reguardless of guidlines to never end without saying close - blah blah. I also can confirm it's not going to the options caller repsonse actions.