So... You’re not syncing with iCloud, backing up to iCloud, or backing up to iTunes? Do you have some other backup method? Because if not, there is no mechanism to rescue lost data.
Computers lose data. Even when it looks like it’s still there, it can be corrupted, or the file system can lose track of where it’s stored. Short of specialized data recover tools (not available on iOS) there is no chance of getting it back. Well, short of a miracle. I hope Apple pulls one off for you, but It seems unlikely.
That’s why backups are important.
I know this probably sounds harsh and lecturing; but that’s the reality. If it’s important, you need to keep in in more than one place.