Afaik, there's no way to "backup" Edge's favorites. You can only "sync" them between devices. If you turn on favourites synchronization in Edge on both mobile and PC then the favourites you create on both the devices will be synced. Hence, if you delete your favourites from Edge on PC, they'll be deleted on your phone too.
To not lose your favourites in future, do this. After creating favourites on your mobile (or PC), turn on synchronization in Edge's settings on both mobile and PC, let the favourites sync and then turn off the synchronization. So, the next time you hard reset your phone, you can easily get all of your favorites back by simply turning on synchronization again.
Hope that helps.