If the flavor was indeed accidentally deleted, then it's unfortunately gone for good.
In Personas 2.0, there is no deletion flag in the tables that store the flavor data.
One thing comes to mind regarding losing flavors though... is it possible that the flavor name was wiped out? I wonder whether you see any flavor in the admin transaction with a blank name.
There was a bug in the admin transaction that has been corrected just one or two regular patches ago which caused the flavor name to be deleted, but the flavor itself was still there in the system. If so, then it is possible to bring this flavor back with a little hacking...