Rename photos to original filename

As you've discovered, you can't rename a file in LR if LR thinks it is missing (with the exclamation point in the upper-right corner). Three options for fixing this:

1. If you don't care about keeping the new names of the files: In Mac Finder / Windows File Explorer, create the folder you accidentally deleted, in the same parent folder as the original. Put the original files back into that folder.  In LR Library grid view, click on each file in the folder in turn, and observe the new and preserved file names in the Metadata panel. Click on the "!" in the upper-right corner of the photo's thumbnail, click Locate, and navigate to the corresponding file in the folder (the file with the preserved file name).

2. If you want to keep the new names of the files: In Mac Finder / Windows File Explorer, create the folder you accidentally deleted, in the same parent folder as the original. Put the original files back into that folder. In LR, click on each file in the folder in turn, and observe the new and preserved file names in the Metadata panel. Use Finder / File Explorer to rename the original file (preserved file name) to the new name shown in LR.

3. If you want to keep the new names of the files and option 2 would take more than two hours and you're experienced with command-line scripting: Use the Any Filter plugin's Sort command to export a CSV file containing the current file name and the preserved file name  (as shown in the Metadata panel) for each file in the folder. Using Excel or a text editor, rewrite that file into a Mac shell script / Windows .bat file that renames the originally named files (preserved file names) to the new names shown in LR.  Any Filter is free for the first 30 days.

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