When I opened Case Merge in our Winter ’27 org, it was switched off, and the retention setting underneath it defaulted to Delete duplicate cases. Turn it on in a hurry and every merge quietly removes the duplicates, along with any easy way to report on them.
We tested it on three cases that Lee Gu at Ridgeline Supply opened for one problem: missing anchor bolts, reported by email, phone and web form. The short answer: turn on Case Merge in Setup, select up to three cases in a Cases list view, click Merge Cases, choose the principal case and its field values, then finish. These are the rules I follow to merge cases in Salesforce without losing history.
Turn on Case Merge, and choose Keep before you save
Go to Setup, type Merge in Quick Find and open Case Merge under Feature Settings > Service. The page says Turn On Case Merge, merge up to three cases into one. Click the toggle; ours read Inactive. It sits with the rest of the Service Cloud case setup, so plan it with your support settings.
Under Duplicate Case Retention, pick Keep duplicate cases. Delete is the default, and deleted duplicates go to the Recycle Bin, where they no longer show up in your reports. The page also warns CRUD permissions are required, so test a merge as a support rep before rollout.