There are several ways that files can become inaccessible to the user.
If the files have been automatically sent to the wast bin then the user can get them undeleted. But if the files are no longer in the Bin, and there was no auto save or backup on the system Then the user could use a undeleting software to recover the lost files.
"BUT" If the files are Vital YOU MUST STOP using the Storage Media that Holds the Deleted Files "NOW"
Because The space that holds the lost Files Will be overwritten With new data by the operating system,if you keep using the device that the storage media is on, and when that happens the Files will be lost forever.
You will need to send the storage media to a
Data Recovery company to safely recover your files.