It's a bit silly to think about replacing Coleman. By the time this is required things have changed, probably more than once. It's very likely we have a new manager, maybe there's been more than one change. Obviously it would be best Silva is here for the next 3-4 years but it's really quite rare.
Assuming Mina is actually good and Holgate lives up to his promise we should be set for CB. Digne was signed for LB. If Bernard is as good as we hope then we have a good situation in the wings, althought if Lookman leaves we might use someone else there as well. Walcott is obviously not getting any younger but if he can stay relatively fit he's a decent foil for Richarlison and Bernard. So the position I expect Brands and Silva are concentrating most is centre forward. Central mid could also well be a position unless Gomes is a revelation (I think we have a loan-to-buy agreement with Barca?). Sigurdsson also needs to pick his game up or it will be another position that will need some shaking.
By the time we get to Coleman there have been unforeseen changes. Some players have been sold because they were so good. Some others dumped because they're not good enough.