Did Windows 10 just delete Windows.Old?

Windows.old is created when you upgrade to a new version of Windows. The contents should be deleted after 30 days. If you havent needed to roll back to the old version by then, Windows will delete the contents of this folder to free space.

I have seen Windows not delete the contents for some unknown reason. I have seen it delete the contents, but not the folder.

So, if your upgrade was more than 30 days ago, more than likely you wouldnt be able roll back to Windows 7.