That would give you "Dum Chicken", an excellent dish on its own, but then it is not BiryaniI agree with aroy broadly.
But on another front and for a variation. You can cook the marinated chicken on dum without adding rice at all, and you would get a chicken dish which would neither be dry nor a curry product depending on the moisture your marinade had and the quantity of yogurt that you added, but make sure that you don't add too much spices in the marinade. Usually we add more spices to take care of the rice as well.
This would save you the chore of making masala which some people find very cumbersome and daunting because most of the people fail in "bhunao technique" and can't do it properly.
The Biryani served in Nehru Place follows this method. The Rice with a lot of oil/ghee is made separately, and the depending on what Biryani you want, they will mix the curry (Mutton, Chicken, Egg or Veg), a versatile innovation, but not the real thing.