It's hard to see this deal will be done with buyback clause, because they (Southampton) want to maximise Delap selling potential within two year if he become world class.
If buyback clause still insisted being inserted then Southampton will be no under obligation playing him regulary in his first season, they will wait until his buyback clause expired playing him in here and there harming his development. I bet if buy back option didn't exist they will try to play him regulary to raise his selling potential to the max.