If between now and the end of the season, Martial can continue with these kind of performances, then going into next season, he should be first choice. Then what we should be looking at is purchasing a back up striker, who is reliable. City have Jesus, Liverpool have Origi, Chelsea have Batashuyi, etc.
We have ovbiously been linked with Haaland, who, although young, is used to playing games and would obviously not want to come and sit on the bench. That said, he's only 18/19, so I cant imagine he'd expect to join such a big club and play week in week out.
If not, players like Callum Wilson or Moussa Dembele would be good cover players.