When properly debeaked, they do not grow back. Sometimes when a large quantity are done at a time and rapidly, it's not done back far enough, just the tip is cut and cauterized, those will grow back.
I personally think debeaking is cruel. Also totally unnecessary for a backyard flock. It prevents them from picking at each other in close confinement. It also kills some baby chicks from shock and some others later b/c they can't eat.
But don't mind me, b/c I'm also against declawing, removal of dewclaws, docking, and ear cropping. Cruel and unusual animal punishment for the satisfaction and approval of humans.