Bebe, Young and Cleverley are, in my opinion, not good enough to be squad players for us and should be sold. We've already lost three experienced players, and depending on who/how many we can sign, that six might have to be close to the lot in regards to who goes this season.
So, after that, the squad would be:
GK: De Gea, Lindegaard, Amos, Johnstone
DF: Rafael, Smalling, Jones, Evans, Evra, Keane, Varela, Buttner
MF: Mata, Carrick, Fletcher, Fellaini, Kagawa, Nani, Valencia, Powell, Zaha, Lingard, Lawrence, Anderson
FW: Rooney, van Persie, Welbeck, Hernandez, Henriquez, Wilson, Macheda
I think we could also chalk off Macheda, Anderson, and Buttner to lower that squad of players to 28 (and then not count the third and fourth choice keepers to give us 26 potential first-team players although a lot of them really aren't). Getting to the potentials who most people wouldn't want to lose, we have Zaha, Nani, Kagawa, and Hernandez. I really think changing too many players at once will be asking a lot for it to click right away, even if three or four of the new players are straight into the first team regardless of who leaves. It'll be the whole atmosphere and how the training sessions go that removing lots of old faces effects IMO (but more-so in the case of the latter names I mentioned).
Up until the last few seasons where our midfield became increasingly weaker, I always felt that we could field two completely different first 11's that would be capable of winning against at least the bottom half of the Premier League. At the moment, I don't think we can do that, mainly due to needing central defence and midfield signings.
Again, it is totally dependent on who and how many come in. We probably need at least four and I wouldn't be OK with say, Nani, Kagawa, and Hernandez being shown the door if we only signed two defenders and two midfielders.
Another interesting thought is how much would you want us to generate from these sales if they happen?
As a worst case amount of losses in terms of personnel with Nani, Kagawa, Hernandez, Zaha, Macheda, Bebe, Anderson, Cleverley, Young, and Buttner going, I'd want the club to at least gain £65million which would be able to account for two top signings such as Luke Shaw + a midfielder such as Fabregas (although I don't think we'll get him obviously).