Is There a Way That Someone Else Can Undo a Paint Delete?

If you overlay any part of an image with any solid colour, be it black, white, red, anything, then save it as a flat file - jpg, png, bmp etc, then no part of the underlying image can ever be restored - so long as the coverage was entire.

See…

You can just about make out bits round the edges where the coverage is not complete, but the majority of the hidden area is gone forever.

I agree with Tetsujin's answer. I would add though, that if you are not sure if your picture has layers or how to remove them, you could always save a cropped screenshot of the edited picture. In this way you are essentially creating a flat copy of the picture AND removing any exif data saved to the original file.