I can confirm that sensors work without a subscription. I let mine expire because I didn’t find it useful. My door sensors and motion sensors still work for automation and notification. I can’t change settings for “tunes” when a door opens, but I have it configured for the two doors I’m interested in.
Without the subscription various settings are no longer available, such as turning on/off the tunes settings for specific door sensors. I never used HMS in a live mode so I never turned on Home or Away so everything was already “off” when my subscription ended.
Update:
Just had the “tune” settings fail on the two doors I was monitoring. Now I have no way to check or change the settings. Posted over here about the issue: