Having done in Desktop, using C# I used the ESRI.ArcGIS.esriSystem .dll and there was a protected override void OnStartup() and OnShutdown method I could use.
In Pro I think the best I can use is ArcGIS.Core.Licensing.LicensingInformation.CheckinLicense(LicenseCodes.'extension') method. I cannot find or think up a way to check if the extensions have been used without the ArcGIS.esriSystem .dll. I also cannot seem to find similar OnStartup() and OnShutdown() methods for the knowing when to run the CheckinLicense() methods.
Has anyone come across something similar to this? I am worried that even with the concurrent extensions, many of my co-workers might just check on the extensions and then never close the program, we have many more employees than extensions.