Excel: Data -> Queries & Connections -> Edit Links

I once encountered an Excel sheet where another workbook/sheet was referenced but Break Link would not work: although I could click the button and Excel reminded me that «breaking links permanently converts formulas and external references to their existing values», the links were not removed.

I was able to find the cells with the references via File -> Info -> Check for Issues, then choosing Check Compatibility which showed a «summary» of cells that contained data validation rules which referred referred values of the other worksheet.

After using this functionality to select the cells with references, I could remove the validation rules in the immediate window with

selection.validation.delete

The updateLinks property of the workbook object can be set to one of the values of the xlUpdateLinks enumeration:

activeWorkbook.updateLinks = xlUpdateLinksAlways

Apparently, some (or all?) links can be found with VBA using the function workbook.linkSources.