If you use DisablePlayerControls to disable the menu controls, you should leave dialogue. So since you're disabling the controls anyway, just disable every single control.
Alright, I'll see if that does it...
Actually, you can just define the topic as a "Goodbye" topic, that should do the trick.
That would make you leave dialogue at the end of the line. I want it to disconnect at the very start of it, but I still want him to say it.
It will be a while until I can test this (I'm still backlogged with voice acting), but I'll post an update too see if it works or if I need more help.