Licensed user-added attachments no longer there



We we off-board a licensed user, I download the sheet access report to confirm whether they own sheets that must be assigned to others. On this one occasion, the licensed user did not own any sheets but had uploaded two files to a group workspace (owned by someone else). The licensed user was removed yesterday and, today, the two files they had uploaded to the shared workspace are no longer visible. It seems as though, once uploaded, the documents should remain (the user's MS account was not deleted, so those documents would not have been). Has anyone come across this before? Is there a preventative measure I can take?

Thank you!