The range is surprising. I've walked to another part of the house and then wondered, where did I leave my phone? Because the airpods just didn't quit.
So if my iPhone was playing music via AirPlay, the alert sound would go to, you guessed it, the AirPlay speakers. Completely pointless.
There was no disruption in the audio. In fact it didn't occur to me until I got back and saw my phone on the table that anything had even happened.