I was by my local Ausländeramt last week to ask about my situation. I've lived here for 27 years and married a German girl here in Germany 27 years ago. My 2 children are German and I have my own house and have always worked. There is no way I'll pass the B1 test as I have never had any need to write correct German as I am a mechanic and work with my hands. I was informed by the Ausländeramt that until brexit happens they can't tell me anything because they don't know themselves. My Aufenthaltserlaubnis was stamped back in 1996 as unbefristet, does this still count? Who knows?