Yes, the previous CMS data re-emerged (the new entries and collection now gone).
It brings up an interesting point: Being able to unlink the CMS data to the design to reattach it to a different collection. After the collection deletion (again, which I did on purpose), those design elements that were associated with it were thereafter locked, and I couldn’t connect it up to a new CMS collection. It had the padlock, and couldn’t be changed, even though there was no collection connected—so I couldn’t repurpose the design to the new collection. It was an orphan I couldn’t give new parents, so to speak.