I was in two minds about releasing this as fixes seems to come slower if there's a workaround. While this isn't strictly a workaround and more of a mitigation as its been a few months now and there doesn't seem to be any movement on this being resolved I threw this together.
Just call cefCleaner.Clean() in your app.open and it will hunt for and terminate any cefsubproc.exe's that were created by your app.
I've tested this on the following but you might also want to test it and implement some error handling.
If you can work it into your app so it runs at the end of your crash detection then that would be even better as the processes will remain running until you run your app again if its only in app.open. If you have it only in app.open at least you won't end up with a silly number of runaway processes if the user keep restarting your app after crashes.
You can also call it when you want and it will terminate and clean up any htmlviewer webkits (best done when the window is closed and not instantiated)
Hope it helps.