Playing a wind instrument after damage (from any source0 to the facial nerve is very challenging at best. If segments of the nerve had to be removed because they were within the tumor, there is little if any chance of regrowth/regeneration. Since this nerve has many branches to various parts of the cheek, jaw, and lips, the amount of paralysis will depend on how many branches were severed. If he can produce any type of seal on the affected side, it might be worthwhile to try playing with the reed slightly to the unaffected side, where normally functioning muscles can "grab on" to both sides of the reed.
Whatever the situation, he will have endurance problems on the affected side, trying to use overtime what remaining muscles he has. Playing should resume slowly, and in the register he plays most easily - usually second space C to open F.
He should also ask his surgeon about the advisability of receiving speech/facial muscle therapy in order to maximize the amount of recovery over time. Specifically, a therapist who has experience with stroke patients and others having facial paralysis.
Hope this is helpful.
Dr. Bill Dawson, bassoonist and teacher
IDRS medical consultant
Past President, Performing Arts Medicine Assoc.
Author of "Fit as a Fiddle: The Musician's Guide to Playing Healthy"