Long term I do think he'll become obsolete, I just don't see the sense in selling him this season, even if we use the funds to buy a midfielder. With Rashford looking likely to miss the start of the season, and Cavani only capable of starting one match a week, I think he'll be needed on the left wing and up top. Despite his poor form last season, he's still a better option than Dan James on the left, and arguably he knows how to play the CF position better than Greenwood.It greatly depends on whether we need the money and whether Pogba stays. As things stand, Martial is second choice striker and third choice left winger. Long term, I don’t see him staying as a back up and I don’t think he’s what we need up front. If the choice is keep Martial and not have the money to spend on midfield, I’d look to sell him. If not, we might as well keep him.
We’ll have to agree to disagree on your last paragraph.