We recently added the ability to transfer ownership to another user when deleting a user’s account from AAD from the M365 admin portal. If no entry is provided, the default will transfer to the manager. https://docs.microsoft.com/en-us/onedrive/retention-and-deletion
The manager or newly assigned owner will have the ability to sync that content or download and then move to a shared library or their own OneDrive.Chris W commented
I'd take this in a different direction. The ability to move the user OneDrive folder into a Sharepoint site would be extremely useful.
For instance, I would use that to script a Staff Termination routing that would do the following:
Convert mailbox to shared mailbox
Remove Office license(s)
Move user OneDrive folder to Sharepoint site used for archived data