If Ghostscript has been initialized, then gsapi_exit must be called before gsapi_delete_instance.

       int ret = gsapi_exit(pinstance);

       private static extern int gsapi_exit(IntPtr instance);

       Private Shared Function gsapi_exit(ByVal instance As IntPtr) As Integer

I found that gsapi_exit is safe to call even if gsapi_init_with_args has not been called.

        int ret = gsapi_exit(pinstance);

    private static extern int gsapi_exit(IntPtr instance);

        gsapi_exit(inst);