Seriously, 5 or 6 out in the next 2 windows and max 4 in? That wouldn't drop the squad numbers practically at all. If we count Robles already gone and Rooney probably leaving then which three or four players would let go and which would you leave? Which of these would you keep: Martina, Williams, Schneiderlin, Mirallas, Bolasie, Funes Mori, McCarthy, Garbutt, Browning, Pennington, Niasse, Besic, Klaassen, Jagielka, Baines, Keane? You have to pick 14 (that's four more to be let go in addition to Robles and Rooney).
Bear in mind several of those players make around 100kpw, or about 5 million per year. Keeping four of them just in case costs the club 20 million for next season.