Without URC situations like this become big problems.
Any projects you can access, go and Check-in Changes on them with URC as soon as possible.
Try and do it often, especially after doing a few hours of solid work.
You will probably have to regenerate the creative island data.
When you look with windows explorer, do you have any content in the islands folder or are they empty ?
If they’re empty your faced with redoing what you have done.
If there is content in your island folder, move it somewhere else, so when you regenerate the creative island data, you have an option to play around with it and see if you can copy the files back in… I don’t know maybe you could check the date created/modified and only copy those .UASSET files back in.
I think you could possibly copy the .UASSET files from those folders and paste them directly into the UEFN viewport
A bit wild but if you make an initial snapshot to revert to if things go wrong, and make a snapshot after each success, you might be able to restore some content if your lucky.