Hi Bart,
By "It was saved in a directory off Office", do you mean that the excel file is saved in local computer, OneDrive or a SharePoint Online library? If it is saved in OneDrive or local computer, it is suggested to post this issue in Microsoft Excel Forum or Microsoft OneDrive Forum for dedicated support. Thanks for your understanding.
If not, you can find the SharePoint Online library path via: FILE > Save As > Select the directory and click Browse in the right pane > the url will appear in the save as box. Try to access the url in browser and see if the file appears there. If not, you may also contact your administrator to check recycle bin and second-stage recycle bin.
Best Regards,
Vincent