I'm ready to bet on Darmian and Mata staying next season.Young isn't deadwood if he is a back-up as opposed to first choice in any position. He can play in the FA and league cups and help out in the odd game against the likes of Burnley, Brighton etc when we have fixture congestion. So keeping Young till 2020 isn't too bad in my opinion, that will be about the time he goes the Valencia way and becomes absolutely useless.
The real deadwood are Darmian, Valencia, Mata and Jones who are of absoutely no use. Out of these, only Jones has been given a contract. The other 3 are likely to leave.
Valencia is going to leave on free though.
Don't get your hopes up for the next summer.