Sanchez obviously needs to go.
Regarding Lukaku, to my mind it's about priorities.
I think I'm right in saying we've targeted four signings in each of the last two summers and in both those summers we failed to make all four of those signings? That gives us an idea of the constraints on the amount of business we can realistically get through this summer, regardless of who our manager is.
Given those limitations, is upgrading Lukaku pressing enough to be one of our main priorities? Whatever limitations he has as a footballer, he is still arguably one of the league's best goalscorers and certainly our best goalscorer. Hardly someone we desperately need to get rid of when signing a RB, CB, CM, RW and/or replacing Sanchez are potentially all on the table too.
It's easy to name players who should be upgraded when there are no constraints on doing so. The manager/club have the much harder job of deciding which of those players have to be upgraded immediately and which he can get something from for now, even if it's not ideal. Lukaku very much falls into the latter category, I think. Particularly as he has shown a good attitude when left on the bench or played out of position.