Jupyter lab: Execute destructors on kernel restart

Let's say I instantiate the following class in jupyter lab:

class my_class(object):
    def __init__(self):
        self.proc = multiprocessing.Process(...)
        self.proc.start()
    def __del__(self):
        self.proc.terminate()

x = my_class()

In __init__(), a process is spawned that opens a PyQt5 window. I have confirmed that del x kills the spawned process, thereby closing the window.

When I restart the kernel of my jupyter lab-notebook, __del__() is not called and the window remains open. Can I teach jupyter lab to execute the destructors of all variables in all namespaces (or even just in global namespace), before the notebook kernel is restarted?