What;s gonna happen is Lukaku will be benched for Rashford up top, when Ole realises, that Rashford is not cut out to be leading man,consistently, it will be too late, to compound the problem, Rashford contract expires next year and don't think there is a 1 year extension, and if Ole drops Rashford or moves him to the left, it might cause issues in the current contract negotiations, the club can not afford to have Lukaku sitting on the bench for a good percentage of the season.
Best move for the club is to cut their losses and sell him for 50 mill with additional fee rising to let's say 58 mill, the same with De Gea, say if De Gea ask to go out on loan, and see's out the last year of his contract.
The lost incured can be recified at a later date.