There are plenty of companies that treat content that was created while you were a premium user differently when you revert back to a free user.

I’m not saying that anyone is entitled to it, I’m just saying that I think the model of ‘content created when I was a premium subscriber can retain some limited premium features’ is a much more graceful and customer-friendly downgrade path.

Forcing all your documents into either public, or a downloadable format you will never be able to edit again even if you resubscribe, doesn’t seem very consumer friendly.