Green is easily replaceable, just get another ageing English keeper or promote a youth player. Bulka already looks good enough, but I could see him going out on loan at some point. I wouldn't be surprised if Green sticks around though, even if he isn't playing.
Cahill will probably be replaced by Ampadu.
Fabregas and Drinkwater will probably leave next season (Drinkwater could go in January) I'm not sure if either will be replaced though. It will be hard to find another player who can come in and play the Jorginho role, there aren't any home grown players I can think of who can play that role. So we may not bother looking for anybody.
Moses will probably be replaced by Hudson-Odoi.
Piazon isn't even somebody I count as part of the squad. He will never play.
A lack of home grown players isn't something I worry about too much. If Christensen leaves, then it becomes a bit of an issue because we would likely need to bring in a new foreign CB and we only have 1 space spare for non-homegrown players. Unless we can find another home grown CB that is good enough to replace him.