There is no way to undo a delete in Photosmith. However, it is highly unlikely for a delete in Photosmith to result in the complete loss of a photo. If you imported the photo from your iPad's Albums / Camera Roll, the source photo will still be there (unless you deleted it there as well). Likewise, if you synced the photo from Lightroom, it will still be in your Lightroom catalog (unless you deleted it there as well). Are you detecting a pattern? The deletion of the source file must occur also for deletes in Photosmith to result in data loss.
The following are the ONLY scenarios where deleting photo(s) in Photosmith will result in compete loss of the photo:
- Imported from Camera Roll / iPad Albums: You deleted the source photo in Photos.app. Photosmith does not modify or delete images in Apple's Photos.app.
- Synced from Lightroom: You manually deleted the source photo in Lightroom. Photosmith does not propagate deletes during sync with Lightroom.
- Imported via Eye-Fi: You also deleted the photo on your Eye-Fi card.
- Imported via FTP: You also deleted the source photo on the device from which your image was FTP'd.
You must make at least one additional delete for a photo loss to occur - and such loss is highly unlikely.