To my experience, he could fly (as passenger) as soon as he leaves the hospital,i.e. 4 to 5 days after the surgery.
I talked about that with a friend who is both neuro surgeon and PPL.
He did the microvascular decompression procedure on italian patients wich get back to Italy from Belgium a few days after the surgery by air.
As pilot you should wait let's say 1-3 monthes before flying as PIC (the surgery may cause vertigo).
I experienced myself microvascular decompression procedure.
I leaved the hospital after 4 days.
I drived my car just 3 days later.
I flew my plane (PA28) 40 days after the surgery.
Of course for the first flights my friend -who is both neuro surgeon,PPL and co owner of the plane- was in the right seat.