If I have an intractable Migraine With Brainstem Aura (Basilar Migraine)... am I likely suffering brain damage? Please be brutally honest.

Honesty is good. Brutality is bad. The likelihood that your headache is an indication of brain damage is very small. Almost zero. But you do need to try to have a conversation w/ a Dr about how to obtain the reassurance you need. I'' refer you to one here.
BRUTAL HONEST. ANSWER NO! There is no scientifically based medical evidence that Migraine of any type permanently damages brain tissue! My opinion only but I hope it helps! Dr Z.