The quest in S.T.A.L.K.E.R. 2: Heart of Chornoby will begin immediately after talking to Varan. The bandit wants Skif to eliminate one of his rivals. In return, Varan will connect the main character with the prisoner who participated in the scanner kidnapping.
Despite having a choice between Shah and Roosevelt, in reality, there are a few more options, although the irony is that it won't affect the outcome.
Aside from the obvious elimination of the leader of the Pack Shah or Voentorg Roosevelt, you can kill both of them. The characters are far from high moral principles, and life in the Junkyard won't change drastically without them. However, Varan will not give you any additional bonuses.
The twist of the quest is that in any case, you will have to fight Varan himself, who will betray Skif later in the story, and this cannot be influenced. That is why you can immediately attack Varan after the dialogue and thus speed up the completion of the extensive quest. The price for this will be just one special gun of Shah, which differs from the standard one by an enlarged magazine, and which you will not find.
As you can see, the variability in S.T.A.L.K.E.R. 2: Heart of Chornoby is very conditional. However, for the sake of completeness, we will describe how to eliminate each of the local bosses.
Shah sits in his own bar, which is not easy to get into. You can, of course, go in guns blazing, but there is a more cunning way. Return to the Junkyard and talk to the local arms and equipment dealer — Guron. He needs to find a lost cargo. This is the side quest Bandit Mayhem. At the end of the quest, you will meet Docent, who will tell you about Shah's secret stash with a special gun. No one else in the Junkyard has such a gun. The stash will be in the Labyrinth area. Take the gun and add it to your equipment, then return to the Pack bar with it. Show the bandit at the entrance the gun, and you will be immediately allowed to see Shah.
The boss will start yelling and swearing, but your dialogue will end in a shootout anyway. You can kill Shah with one shot. The other bandits in the bar do not pose a significant threat either. Don't forget to pick up the boss's PDA as proof of the completed task.
Before going to Voentorg, pay attention to the optional part of the quest — talk to Borodulin. Go to the location and meet Colonel Borodulin of the Duty. He is a completely unhinged guy who loves to drink and strange entertainments. First, he will suggest shooting mutants. Several fleshes and boars will run at you. Dealing with them will not be difficult. However, after that, the colonel will offer a new game — you must survive for a minute while Borodulin hunts you. If you survive, he will tell you a secret way into Voentorg. Agree, because completing this quest is easier than it seems. Just run across the road and stand behind a tree; the colonel will lose sight of you and will spend almost all the time just looking without shooting. When Borodulin says he's had enough, talk to him one last time and learn about the pipe system that runs around the entire Voentorg building from the outside. The colonel will also say that Roosevelt is actually a jerk and his words should not be trusted.
Upon reaching Voentorg, you will quickly find the pipes, but it's not actually necessary. Just enter the building and talk to Roosevelt. He will immediately realize that you came to kill him and will offer to pay for his life. However, he will refuse to give the PDA. Here you can easily agree, because, again, the game doesn't care about your specific actions.
Agree to the payment and leave the base. As soon as Roosevelt transfers the coupons, return. The man will magically disappear from his office, and he won't be in other parts of the base either, but there will be a backpack with the very PDA behind the desk. This way, you get both the money and the tablet without killing anyone. There is an option to simply shoot Roosevelt, but then you won't get the coupons. You can now return to Varan. The quest is complete.