If Pogba goes, then there goes your link to Fernandes and the forwards. Camavinga is not a playmaker, atleast not yet (he is 18). van de Beek was also brought in to replace Pogba, so if Solskjaer starts trusting him, then okay. Otherwise, only a DM is pointless, it'll be similar to McFred w/o a creative presence in the midfield. With SMS, atleast he would carry it forward and provide a link and combine with Fernandes, Rashford etc.
Also, playmakers from deep are **** expensive. We have needed someone who could dictate tempo for a long, long time (since Carrick), but they are few and far between, and a lot of them are unavailable. Frenkie de Jong, for example, is an excellent option, and after his initial struggles, has come in leaps and bounds, but there will be a host of teams queueing for him when he decides to leave. Tonali is another to look out for, with a similar profile to Carrick (Regista/DLP).
If Pogba leaves, you'd think the profile to be targeted is Aouar/SMS, who are creative and can also carry the ball from deep. Without Pogba, our midfield is purely functional and pretty boring. You definitely need a like for like replacement. A proper defensive player is needed, sure. But not at the cost of one or the other. You need creative and goal threats from all sides of the pitch, only then will it be truly effective. Can't always just pass it to Fernandes and hope he pulls magic out of thin air.