As has been said, Jose isn't getting rid of him. Martial wants to leave. Jose's always said he just won't stand in the way of players who want to leave, as it should be. Keeping unsettled players will never be good for squad harmony etc.
He's behind a player who is simply better than him at the current moment, whether he will become a better player in the future and what not, I don't know, but as of now, Sanchez is a superior player, who offers more to the team, who also suits our style and tactics going forward more. I'd wager if we were to win major trophies next season, he'd have a big part to play in them too.
If Martial doesn't want to wait for his chance that's completely in his right but it's not Jose's doing. He had the opportunity to sign one of the best players in the league, no manager would turn that opportunity down for a player who is still young and who still has a lot of flaws in his game. Pep was extremely interested in Sanchez on two occasions, the summer and Jan, even with how good Sane and Sterling were for them, one of those two would have been in a similar situation to Martial now, as is the case with many young talents around the World at big clubs.
He will get chances like all players will, but if he wants guaranteed game time, he's at the wrong club. All this nonsense about him not needing to contribute defensively or work off the ball is crazy. It's the top level of football, some of the teams that the majority on here cream themselves over are in part so enjoyable to watch due to their movement and energy. Firminho is probably the hardest worker in the league. To want that sort of entertainment but to be happy watching Martial stroll around the pitch whenever he doesn't have the ball at his feet makes no sense to me. There's more to contributions off the ball and defensively than simply 'tracking back'. There's the positional aspect, closing down of players, making runs off the ball into the channels etc. These are all aspects of the game where Sanchez and yes, even Lingard are better than Martial at. This isn't taking away from his immense talent, his ball control and finishing are top notch.
Like I've said, I'd be gutted if he leaves because he can be a top player, but if he does he won't be the first or last great talent that didn't make it here. We've been fine losing far better players in the past. If he really wants to leave, there's no point keeping him on. If Jose manages to win some proper silverware with his replacement next season, his decision was justified, if he doesn't and Martial does so with his next team, playing a huge part, then his decision wasn't justified and I'm sure years later people will still be giving him shit for it just like with KDB and Salah etc. which i've read a trillion times on here now. Regardless, his criticism would be deserved and we'd be fine, we aren't strapped for cash and there is a plethora of young talented players and there always will be.
Also people saying we should keep Martial because Jose might not stay for long have a point. Although that's what's always going to happen when the board is intent on giving managers full control of squads yet refusing to implement a DOF system. Managers are always going to think of ways to win in the now, especially with how competitive and short-term the sport is becoming. They need to win because it's their job on the line and realistically they'll only get what, 2-3 years with a team?
The days of the SAF's and Wenger's are gone. Managers come in, need to implement their ideas quick and win. Not sacrifice important aspects of a team just to simply keep a young player happy that they probably won't ever work with again. If said young players meets their criteria, they'll play, if they don't, can you really blame managers for opting to go with players who they think will bring them success? They should then rightly be judged on whether or not it was the right approach.