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.Anonymous commented
Definitely an issue for my group as well. Our department is specifically designed to have "flow-through" of employees....not staying much longer than 2-3 years.