When you use one of the LaunchApp functions (LaunchApp, LaunchAppAndWait, LaunchApplication), you get a return code. However, that return code only shows the result of InstallShield executing the command.
If InstallShield was successful, you will get a return code indicating success, which is ISERR_SUCCESS. If it was not successful, you will get a value less than ISERR_SUCCESS.
Here is a code snippet showing you how to get the actual return code from the command being executed:
See how easy that was.