It's a very precarious situation all round really. For reasons others mentioned regarding team harmony - if Martial gets shafted again for another big name, we really will have lost even the remote hope he can come good - as well as his ego and powers of influence on and off the pitch plus the notion of him grafting in a World Cup year, where he'll be saving his legs for a last hurrah... on top of that, him not accepting rotation or being a sub...
It's a potential minefield, for sure. I think he'll want to exit mainstream football on his own terms - if he ever goes back to Sporting as a player, it'll be when he's absolutely done, and accepts it, not whilst he's still able to hit 20-35 goals a season at the top level.
ten Hag looks like a perceptive guy, so I hope he has contingencies and plans in place no matter which avenue things go down. He really doesn't need a circus during his debut season.