4. I have two theories as well, as why Tchort doesn't let you leave. It makes sense if he wanted Six, he would let you leave so Six or the faceless would have to come to him themselves. My first theory is; is that Six was masquerading his presence on top of yours. Simply put, Tchort didn't know it was a normal human that fought their way to him until you enter the chamber, as he comments his was expecting the high one to come himself. This makes sense because when you are in DC, Six only talks to you face to face, never over radio, never using psionics or anything else. This means Tchort could never tell your presences apart because Six never gave them a way too. I also think this is a possible reason why Six doesn't assist directly during the events of DC. But I believe he was watching and putting his presence on you as an indirect form of assistance. The other theory, which is extremely unlikely, is that Tchort was afraid other God Men being able to come down after knowing what was going on via your character returning from DC. So Tanner, or maybe Dude (who i'm convinced is a god man). But that's way less likely to to be the case.
Your post is backed up pretty well by dialogue with the Faceless Commander. Although I dont think the Faceless would ever let themselves be captured alive ... It would be in-character for them to self terminate rather than let Tchort peek into their hive mind and everything they collectively know.
Interesting point about Tchort thinking Six was the one turning on the power at Arke and opening the gates. I'd never though of it that way.
I am still confused by the line, "It is Shadow we expected" though. Some have made the connection between Shadow and Rahm-
Umbra, yet we are not Six, the one Tchort supposedly expected, confirmed by the "mangy railrat" line soon after. The English in UnderRail has improved alot over the years, and Tchort's monologue has even been rewritten a few times, so I don't think "It is Shadow we expected" can be written off as dodgy translation. Maybe epeli has some theory explaining that, having seen all the iterations of that fight since release.
The other thing I wonder is the status of the third Godman. Did he get integrated into Tchort? It would explain Tchort's knowledge of High Ones & the Cube, as well as why Six knows it must be destroyed (could also have Cube knowledge from Biocorp technocrats though). And since Expedition, we know killing fully fledged Leviathans is not impossible for non-Godmen. Or maybe Tanner's "crime" was murder? I had thought the third Godman would be revealed during Expedition, but they are maybe saving the reveal for some place in the West or East? Who knows.
Anyway, enough rambling for now.