HP ProDesk 400 offline missing ethernet network adapter

Possibly the strangest call for a while ... a cat stepped on the keyboard and the computer went offline! Tried all the obvious fixes for airplane mode, reset network, troubleshoot network, BIOS, etc, then spotted there was no ethernet device in the Network Adapters section of the Device Manager. Just the WAN Miniport drivers. You can see in the image a typical list - the Realtek is the ethernet cabled network connection. GBE stands for Gigabit Ethernet.

Looking under View > Show Hidden Devices revealed the Realtek driver, greyed out, not recognised by Windows as a current device. Updating the driver didn't recover it. Uninstalling it removed it completely and it didn't come back when clicking Scan for Hardware Changes.

The fix was to reload the driver from the latest HP download (transferred via USB flash drive from an online computer)
https://ftp.hp.com/pub/softpaq/sp95501-96000/sp95572.exe

Realtek Ethernet Controller Drivers version 10.32.1206.2018, dated 9 Apr 2019, at time of writing this.