The most important thing you need to know is that while the data is still physically present on the storage device, it can be recovered by fixing the deleted logical links, which will make the files available again. I found a way how to recover deleted files from a USB drive on Mac using this great article. Eventually, when the operating system needs space to store new information, the original files will be overwritten. Once this happens, the recovery program will not be able to recover your lost files.