Was there ever a published process or geoprocessing tool to cleanly remove a Utility Network from an existing enterprise geodatabase? We are iterating through schema changes in our test environment, and have attempted to delete the UN. We weren't successful and have gone back to a restore point as a result.
From what little we've found on this scenario - it seems like an entirely new database (Oracle) and enterprise geodatabase may be the best option. This is especially true given that this is a test environment.