Well we've got 3 positions to cover if we play 4-3-3 and 2 if we revert to a 4-2-3-1 which would be more ideal against smaller clubs. For 4-3-3 we would have Schneiderlin, Bastian, Herrera, Carrick, Blind, Pearson, Harrop and Perriera. Also Di Maria, Jones and even Rooney can do a decent job there (Di Maria best games at Real were in CM). Assuming we're adding a quality striker which we probably will, if we revert to 4-2-3-1 we would have Schneiderlin, Bastian, Herrera, Carrick and Blind + three quality no 10s in Mata, Januzaj and Rooney. Di Maria can also play behind the striker and so can Depay and Young if needed. That gives us plenty of options.
As said Fellaini made himself important due to his physicality which our midfield lacked. This weakness is mitigated with the signing of Schneiderlin, Bastian and the return of Pearson. Rather than see Fellaini end at the bottom end of the pecking order and lose value because of it Id rather see us sell him now and bring other players like for example another right winger. That would release Mata and Januzaj from the RW role and in their natural role and therefore allow Rooney to play upfront.