Hey bobtilla, from your post I cannot be sure where your addons are located on your harddrive now.
Where exactly (folder path) are they lcoated?
They should be somewhere in c:\users\<your windows username>\documents\Elder Scrolls Online\AddOns\".
Check this link:
http://wiki.esoui.com/UserFolder
Be sure to check the screenshots of Ayantir abvove and read + understand how Microsoft OneDrive is working and how it interfers with the ESO addons (forum search: onedrive)