Some of these are tricky ones.
I actually expect Ashley Young and Ander Herrera to be offered new contracts, but not long ones. Young's could be as little as a 1-year + 1-year extension option. While Herrera would probably be two or three years with a +1. Herrera is somewhat dependent on Fellaini and McTominay though, IMO. The long-term plan should really be to move those guys on before Ander, with Ander likely be sold towards the end of whatever new contract he is offered (if he is).
Phil Jones should 100% be released, the club shouldn't even debate it IMO. I'd even wager it could be worth flogging him at the end of January if our other four CB's are all fit by then. He's been a terrible investment, thankfully we were able to keep him on somewhat low wages for us during his tenure. Sticking with defenders, Darmian is a cert to go in the Summer, I'm a little surprised he's still here now. Valencia is another odd one, as the club may repay his loyalty, but I think he'll play out his last season as a back-up fullback. Shaw will keep the left back slot, while I think it'll be more a case of Young & Dalot fighting for right back, unless there are injuries or Shaw needs resting in which case Young goes to left back and Dalot right (Valencia on the bench). I would expect it to be made clear to Antonio that this would be his role, and if he doesn't like it and wants to play, he'd probably move in January to get us some return.
Juan Mata.. I think will go. He's such a likable guy, he gives us a lot from set-pieces and does contribute to the side. However, I think he has just never really fit into the way we've played under any of the managers he's played under (which is odd considering how good he was at Chelsea under Mourinho). It always seemed like we tried to buy more players who liked to play at no.10 instead of playing him there. I hate to sound disrespectful as he's a very good player, but sometimes, particularly in away games with him out wide, it felt like we were playing with 10 men. He should look for a new challenge and unfortunately, it might be at a club who won't be challenging for trophies. If he stays in the Premier League, it'd have to be somewhere like Leicester or West Ham.
So, in summary IMO:
Young - New Contract (One-Year Rolling)
Valencia - Sold in January 2020/Released June 2020
Mata - Released June 2019
Herrera - New Contract (At least Three Years Total)
Darmian - Sold in Summer 2019
Jones - Released June 2019
Everyone else either has or will be offered long-term, improved contracts that they hopefully accept.
There are at least a couple of players in our squad on long contracts that should leave before some of the above.