Somehow, I managed to delete a folder containing about 100,000 photos which are stored in OneDrive. Recovering them is hideous because OneDrive only allows you to restore the files which are presented in the Web interface, about 100 at a time, so it's not very practical, but fortunately they're also in the PC's Recycle Bin, so I used Recuva. It was brilliant, and recovered about most of them, but I still need to recover the several thousand from OneDrive.
What would be really useful at this point is to be able to save all the information in the Recuva interface into a csv so that I can use sort and filter in Excel to identify them, but the text file saved in Recuva only lists the files' paths and sizes, not the status or the other information, so I'm going to have to keep the Recuva interface open while I work through the overwritten files, and if I close it, I'm stuffed because I'm now of necessity overwriting the disk space previously used by the deleted files.