HomePod does persist Airplay connection with AppleTV as long as you don't Airplay directly to HomePod from a separate source. You can still Airplay to AppleTV that is Airplay'ing to HomePod but that will turn on your TV. It's not perfect but I have enjoyed using HomePod as my primary AppleTV speaker since launch and hope they introduce multiple Airplay streams with Airplay2 release.