There's permanent and there's permanent. What's actually healable and repairable if you have the money, connections, and favor of the sect, and what's healable if you don't, are completely different. Crippling his spiritual and physical cultivation such that it would take thousands of stones and the intervention of a friendly expert might not technically be permanent, but it will effectively be. And then his use and potential in the sect vanishes, and he get sent off to his military service.
Meizhen is perfectly capable of permanently crippling him, leading to his death, without technically doing either.