After performing migration, neither WSDL URL nor Web Service URL would change. WSDL URL would only be used to retrieve the structure of the web service at the time when you create the dashboard. Once you have the imported the WSDL and have the structure of the web service imported, the WSDL would not be used.
When you view the dashboard on portal, the dashboard would only refer to the Web Service URL in order to refresh the web service and pull data from the reporting database. Your dashboard would work even if you remove the WSDL URL. Though it is not recommended to do so. Please refer the below screenshot.
Hope this helps.
Regards,
Niraj