Left vertebral artery occluded?

[Whysundaes]

My dad is 60yr old -4yrs ago they made an accidental find in an mri his left veterbral artery was occluded- at the time they suspected he was born this way being his right one is dominant and much larger than average.  Fast foward 4yrs today he suddenly starts to experience spinning sensations, dull headaches in back of head and ringing in ears along with numbness in face.  Bring him to ER they did a ct scan of head and found an old stroke and pretty much said it was no big deal.    3 weeks later spinning is still going on he wakes up in mid night and has an ischemic stroke.  Back to the Er and mri confirms a stoke in mid cerebral artery in brain.    

Is there anyway the occluded vertebral artery can be an issue here?  Is it possible that the blood that flows to the occluded
Artery coagulates kicked back to the aorta with plaque from
The occluded artery sending a clot to brain?

He’s on Coumadin and a statin now.  He tried plavix but was allergic.

Can you live a Normal life with occluded vertebral artery?

Please any help much appreicated