PyQt - how to detect and close UI if it's already running?

I'm starting the UI from within Maya. If the UI hasn't been closed, running the UI again will completely freeze Maya (with the error "Event Loop is already running")

Manually closing the UI before re-running the script will prevent it from freezing up. But I guess that's not really practical.

Is there a way to detect if the UI I'm trying to run already exists? And possible force close it?