Schofield doesn't lose consciousness when the German sniper shoots him in Ecoust-Saint-Mein. He's killed.
The German dies without regret, having accomplished what he intended to do. Because Schofield died without fulfilling his promise to Blake, he returns as a ghost. Every character he interacts with after that is a ghost as well. The living don't notice him. That explains a number of discrepancies, like the disappearing wound and the fact he has a pack full of food when he needs it. The attack at the end is only called off because the first wave (including the popular Lt Blake) got slaughtered without taking a single objective. Also, the battalion commander and a lot of his staff were killed in the shelling and none of the surviving officers were keen on pressing the attack. Need further evidence? Cherry blossoms are a symbol of death. Rivers are symbols of death. The song "Wayfaring Stranger" is about the merciful peace of death. And in general, the movie gets very surreal after Schofield loses consciousness. The only reason Blake didn't return as a ghost is because Schofield told him he was dying, which gave him the chance to accept his fate.- It's an awesome theory, but the first wave was already in the process of getting slaughtered when Schofield shows up—thus the run across the trench. It's not impossible Colonel Mackenzie would have called off the attack if everyone in the first wave got killed, but it seems very unlikely. Unless it was all part of Schofield's Dying Dream—what he wished he'd accomplished before he was shot.
- Consider instead Schofield survives through the entire film, but dies at the tree of exhaustion, exposure, and a pretty viscous head wound, having pushed himself to his breaking point to complete his missions. The hidden cut panning around the tree and the sudden warmer, more surreal color palette seem to indicate that this isn’t the Real World anymore.
