Would anyone pull a Pied Piper and choose to destroy the thing rather than let it be subverted? I know that's not exactly what PP did, but would a decision like that only ever happen in fiction?

It wouldn't need to. As sibling commenter pointed out... they'd have a massive exodus of talent, and they'd cease to make progress on new models and would be overtaken (arguably GPT 5.3 has already overtaken them).