There is no single tool to convert a BAG dataset to XYZ. However, you may use the following tools together to achieve that result:
Raster to Point tool (Conversion toolbox): Use this tool to convert the BAG file to a point feature class
Feature Class Z to ASCII (3D Analyst toolbox): Use this tool to convert the feature class obtained in the previous step to write to an XYZ file
If I may ask, is there a reason why you need to convert the BAG file to XYZ? ArcGIS can natively read a BAG file and you can run raster analysis tools on it directly.
