Knecht would renounce Castalia.

At least he did walk away from it at the end The Glass Bead Game.

I think he wanted to get away from that sterile hermetic bubble, which did have some fine features like the devotion to music, art, past scientific discoveries, etc., but was a closed system. One could infer that he wanted to get back in touch with the real world of nature and a way of life that evolves socially and intellectually.