If you enabled it, then it will have sync'd your Desktop and Documents folders to iCloud Drive.
If you disable the feature, the local Desktop and Documents folders will be restored to your Home folder, but they will be empty. You must then copy the files from iCloud Drive into the folders on your Mac.
Your Desktop and Documents folders actually are never moved or deleted until you disable the feature. They remain in your Home folder, but Finder doesn't show them there. It shows them in iCloud Drive instead.
I just enabled Desktop and Documents to test this out. I had lots of Pictures in folders on my Desktop, so it couldn't complete the upload. I waited until some of the documents had been sync'd.
I disabled Desktop and Documents and found that it restored my empty Desktop and Documents folders (after a short while--there was a short time where they still showed some documents). When they were empty, I moved the files out of iCloud drive and back into the folders in my Home folder.
The iCloud Drive folder had a Desktop and Documents folder showing and inside them were folders specific to this Mac. All of my documents were inside those folders. I moved those back into the appropriate folders in my Home.
This was merely one test, but it appears you can successfully disable Desktop And Documents while it is in the process of uploading to iCloud, then move the files back into the normal locations.