Will Solder show up later if you leave him alive?
Then, you have the option to either kill him, or simply knock him out.
But which is the best choice?

Warning: minor story spoilers follow.
Should you kill Solder in Stalker 2?
There are no immediate consequencesto killing Solder during the “Behind Seven Seals” quest.

If you keep Solder alive, he won’t appear until quite a lot later on in the story.
In other words,it’ll be many hours before you see him again.
We won’t go into the details of this later quest to avoid unnecessary spoilers.

That is, if you’ve got the option to stomach the idea of not killing him.
But if you do kill him, you don’t get anything major out of it.
I leave it in your capable hands, Stalker.