Unfortunately, even at the database level, there's not a way to restore relationships from a previous state or snapshot. However, while a restoration isn't going to be possible, there are ways to create relationships en masse that may be useful here and make the job of recreating these relationships easier.
This first of which is our Import Relationships plugin. This would basically let you use Excel to enter the upstream and downstream Item IDs into two columns within a CSV file and then import that to create those relationships as needed. You can learn more about this option here.
And the second option would be to actually use our relationships endpoint with the API to create new relationships as needed. This would most likely be a bit more work than the Import Relationships plugin, but again, if you wanted to, you could basically script the creation of those relationships via the API. We can't work on those custom scripts for you, but you can learn more about this here.
Again, I'm sorry that we can't restore those deleted relationships, but I hope that one of the above workarounds to let you recreate them with ease will help.
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