Whenever Videopad is closed, after changes have been made, it will prompt to save. That becomes a VPJ file (not playable). Search for it on the PC.
If there was a crash, an autosave may be found in C:\Users\[user name]\AppData\Roaming\NCH Software\VideoPad\autosave.vpj
Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, that choice is available by clicking the caret to the right of the Save Project button on the toolbar. That's your protection.
At least one VPJ file should still be on the PC. Find it and double-click it to reload the project.
The exported mp4 can be loaded into Videopad and further edited, but it will be a single file - no individual clips.