You could expose data from your Mendix app as OData. Excel can read that data and refresh that data when that Excel sheet is opened again. So when you change the data in Mendix the Excel refreshes the data through the OData service. And yes that Mendix data can be in the cloud if you opt for the standard Mendix package. But Mendix can be hosted also on premise so it depends on where you want to deploy your Mendix app.