What iOS 13 and iPad 13 bring is what is called persistent HotSpot. Simply put, that means the HotSpot connection to your iPhone or iPad with an LTE data connection will stay on. And that means your Mac or iPad or whatever is connected to your cellphone connection via HotSpot will also stay connected when the devices go to sleep, and that means you still get incoming messages and email.
Wonderful. With caveats.