You cannot predict when an app would be tombstoned in Windows Phone. But still you can simulate it by enabling a settings in the Property page of the Windows Phone project.
- Browse to the Property page of the Windows Phone project.
- Select the Debug tab.
- Select the Tombstone upon deactivation while debugging.
- Build and Run the project.
- After the app launches, click on the Windows key to deactivate the app, there by tombstoning it.

