If you feel that he has vital knowledge of the Blight and of Mimsy's magic... (voryn starts, already winded. not eating for fucking days and being sustained by treebark and sheer will takes its toll on a person's stamina.

whew. okay.)

... Then I believe we should interrogate Mister Tibbs, thereby manually exhausting his usefulness.

Keeping this creature alive would give him opportunities to escape or for others to free him. If Mister Tibbs is crucial to us, Mister Tibbs may be crucial to others—we cannot let him live.