We need to get a new striker if he leaves. We have Cavani, Martial, Rashford, Greenwood and Sancho for 5 positions (not including youngsters like Diallo and Facuno). With Greenwood still a kid, Sancho needing to settle, Rashford injured and Cavani not able to play every match, we need to keep Martial.
He did not fulfill his potential, but I would rather want him on the bench than James or Lingard. It is going to be a long and tough season so unless we sign a striker, Martial will stay. And if he can get back to anything close to 2019-2020 season, good for us.