Delete them too
Screen: Rooms
What it is
A button in the Delete <room>? box, shown in place of Delete room when the room has sub-rooms. The box lists them under Its sub-rooms.
What to enter
Press it to delete the room.
What it changes
In the app: The main room and every sub-room are deleted, with all their devices. They are gone from every phone after the next Save & Deploy.
In the house: After the next Save & Deploy the hub no longer has the main room or its devices, or the sub-rooms and theirs.
If it goes wrong
Deploy history keeps the previous version. If the room changed while the box was open, nothing is removed.