I think your suspicion is correct. I have had to manage my Cranio-Cervical Instability (CCI, otherwise called AOI Atlanto-Occipital Instability) the ‘conservative’ way, i.e. with a Philadelphia collar (fixed to a body brace for quite a long time) in fact I still use a Johnson CTO (big metal head and body brace) as well on a nightime – the latter mainly to stop the pillows from pushing my head forwards. In the abscence of fixation surgery, you need to seriously consider this option, it’s vital you support this area and help avoid any movements that will exacerbate the already injured area.
Regarding the VA (Vertebral Artery) I had a suspected partial dissection of my left vertebral artery following my flexion/rotation injury and, as this artery threads up through each vertebrae, looping over the top neck bone C1 (Atlas), then into the skull, I can understand why this vessel is particularly vulnerable. You say your VA was occluded as well as your ICA (Internal Carotid Artery) and I can see them in the scans but I’m not used to reading these type of scans so, can you identify anatomically whereabouts in your neck/head these occlusions occur?
I also think you should consider how else you can mitigate these circumstances as much as possible, i.e. by regularly taking Omega 3, or other supplements that help to maintain blood vessels and circulation (if you’re not doing so already).