I recommend a nightly job the exports all content from the console and checks in the XML data into a GIT repo. This lets you track changes over time and makes it easy to restore specific items, even if it is back in time. You would be in much worse shape if someone modified all of the fixlets & tasks before deleting them.
I wonder if this operator was not malicious, but wanted to have the effect of “locally hiding” the items, but didn’t know how to do that, or didn’t know that deleting them for themselves would delete it for everyone.