Waterloo road has always hadd characters come and go, it keeps it fresh and is probably one of the bbcs cheapest shows per episode, hence why it is usually 20 episodes a series.
I don't know how long the break is (just said it's back in Autumn lol) and it will probably start a fresh next "term" so just don't expect it leading on from this series.
Also did anyone piss their selves laughing when grantley was like "BROTHERS AND SISTERS, I HAVE COME AND JOINED THE STRUGGLE!".