We are not a big Mac shop so we can't have terminated user's machine laying around for 2 weeks+ in case the manager ask for data from terminated user's Mac. We were able to get around this by taking the full disk image using Disk Utility but this feature seems to be impossible for Mac with T2 chip.
Here is the steps I usually take the disk image. 1. Place the terminated user's Mac to a target mode. Connect to Mac Mini using thunderbolt 3 cable. 2. On Mac Mini, open Disk Utility. The disk from terminated user's Mac is detected in Disk Utility. 3. Unmount Macintosh HD, Select APFS container and go to File > New Image > Image from "Container disk1"
This process takes a complete backup of Mac disk in DMG format.