We need a phased approach over 2-3 windows, but there is a lot of deadwood to clear out.
Replace ASAP
Darmian - Not good enough.
Jones, too injury prone, decent when fit; but that's rare - so need to get rid.
Rojo, decent CB, but we have enough decent ones, we need a WC one, surplus to requirements.
Mata, was a great player at Chelsea, was decent at times for us, just does nothing for us anymore.
We need a proper Right Winger, a top class centre back immediately. The guys above need to move on to get those people in.
Replace Soon
Herrera,
Fellaini,
Lingard,
Valencia,
Young,
The midfielders need to be replaced to improve the overall quality of the squad/team. They don't push the "first team" guys hard enough, and when bought on are limited in what they do. Right now we see Pogba/Sanchez stinking the place up, Matic is hardly pulling up any trees either, but the replacements aren't good enough. Your backups need to be good enough to replace the first team when they're not in form, ours aren't.
The fullbacks are just ageing and are currently being pushed out of the squad by younger replacements. Long term we need to consider replacing these guys either with first team quality FB's or backups to push Dalot/Shaw.
Wait and See
Pogba, Does he want out, or is this just limited to Mourinho. If he's inconsistent under a new manager, i'd sell whilst his value and marketability is high.
Sanchez, Out of form, or finished? We need to take some time to tell. If he is declining, we need to ship out.
Martial, is he being held back, is he misused, is he just lazy? We need a new manager to give him a run and find out.
Bailly & Lindelof, i thought one day these guys would be our Rio and Vidic, whether they can remains to be seen. Need to give them some time to develop, build a partnership. If by summer 2020 they're still shite, get rid.
Lukaku, I'm not saying we need to replace him but in his careers he's always had highs and lows. During the low periods he doesn't score, we need to consider where the goals come from in the team when this is the case. Maybe that's rotating in Rashford/Martial as direct competition, or buying in a striker for that purpose.
Some of these guys are out of form, others might be stalled in progression, we need time and a fresh pair of eyes to see how it goes with them.