He will still need replacing in terms of pure numbers. Foden might be his heir but Fodens already in the squad, we will need an extra player to replace silva next season. Likewise, assuming this is Fernandinhos last season he will need replacing too even though we’ve just signed his natural replacement.
Pep might have different ideas as to how to replace them, for instance we could see Bernardo move centrally permanently and we use silvas space to bring in a wide/forward player but either way there’s at least one, likely two and possibly more if gundogan doesn’t extend who will need replacing next season. I think there’s a very good chance we will make at least 1 signing for next summer this window with them staying elsewhere until then just to cover ourselves.