When the bolt comes forward, it pushes a round out of the magazine into the breach. The ejector hooks over the end of the casing. When a round is fired, the spent casing is forced backwards pushing the bolt backwards too. The ejector holds everything in place, mainly the rear of the casing down against the magazine spring. The next round/follower in the magazine provides spring pressure under the spent cartridge so as soon as it clears the breech, it's pushed up and away. The next round is pushed into the breach by the bolt and the process starts again. The Mauser C96 works more like a semi-auto rifle (having a bolt, ejector and integrated magazine) than modern semi-auto handguns that have a slide.
Things missing on a Denix: Breach, Follower, magazine spring. Also, probably anything from keeping a follower from falling out of the top of the magazine.
What he said ^. I don't think it's worth trying to make a Denix this operable. Take the easier way and just mill out the shape of the extractor. No one will know but us.