what do you mean by footprint?if there's no footprint there's nothing for google to detect, so yes, you can "recycle" them. But if there's any minor footprint all of your sites (both the PBNs and the money sites) could get de-indexed
deleting the content means nothing. Google tracks a lot of things, and unless you handle most / all of them you're bound to get caughtwhat do you mean by footprint?
i delete all of the content.