There will be more current players remaining in 5 years time than there are players remaining five years ago. That is because in SAF's last few seasons he placed a lot of importance in the elder statesmen - Scholes, Giggs, Rio, Vidic and Evra keeping out younger players who as a result decided to move on, and buying RVP as a short term signing (which you could argue was part of why Kagawa and Welbeck moved). We also had some young talents turn out completely shit of their own accord despite many opportunities like Anderson, Cleverley, Gibson (you could arguably add Welbeck to this category too), I don't think it's hugely optimistic to expect a few of the current youngsters to fair better.
My guess:
Highly probable:
Herrera
Shaw
Depay
Smalling
Jones
De Gea
Likely to stay 3-4 years but current age means likely to leave in 4-6 years time:
Mata
Rooney
Carrick
Possible depending on individuals' development:
Januzaj
McNair
Pereira
Wilson
My guess:
Highly probable:
Herrera
Shaw
Depay
Smalling
Jones
De Gea
Likely to stay 3-4 years but current age means likely to leave in 4-6 years time:
Mata
Rooney
Carrick
Possible depending on individuals' development:
Januzaj
McNair
Pereira
Wilson