"Marcus doesn't live alone, does he?"
Is this just a case of right answer, just not added yet? Or am I completely wrong? Because as I understand it, this is the implied "I assume the answer to this will be no" and the opposite would be "nonne" meaning "I expect the answer will be yes."
For my money, yes, that seems equivalent and should (eventually) be an accepted answer. Report it, if you haven't already.
No. It's definitely a question and it includes the assumption that Marcus DOES NOT live alone.