There had been some rumblings about retirement before the accident. He's also not getting younger. I'd be a tad bit concerned about family medical history (Dad "Bud" had Alzheimer's) as well.
Volde, I don't know if you remember EriksT. Used to post here frequently. Right after his dad died (shortly after Sully debuted with the Preds), his mom had sudden bouts of memory loss. Dementia set in rather fast - and she wasn't "old and decrepit" by any means (she was roughly 65, just retired - though not willingly). The last handful of years of her life were horrible, and it's one main reason why he's living with an uncle in MKE.
I'm not saying a traumatic event would cause something like that in GMDP - that's for people who have letters other than "BS" behind their names like myself to guess and determine. But any sort of impact that close to the brain - and one that screws up your visual cortex - can have a traumatic effect on the system.
It wouldn't surprise me if he did resign or "move upstairs" during the off-season, and hand the full GM duties over to Fenton or someone else.