Considering Lichthammer's powerful psychic abilities, how could she not know that Church hatesbeing calledWilhelmina? (Although it is perfectly possible that she was simply panicking and not utilising her powers properly, given her situation.)
Lichthammer is a an utterly sadistic monster that enjoys preying upon her target's mind and body simultaneously. She probably DID know that Billie hates being called that name and why. What she probably DIDN'T expect was that it would blow up in her face.
If each previous Jericho team (the Blackwatch commandos, the Templars, etc.) had to reach the breach at the Sumerian level in time, how is it that Lichthammer, Maltheus and Cassus Vicus are all still alive and well (figuratively speaking)? Or is it that the Firstborn just recycles them back into being as they were, like all of the hundreds of enemies that you face? Also, if being separated into six or seven pieces didn't kill Antadurunnu, how did being shot in the face? If he was so easy to kill, why didn't the Firstborn just do it to begin with to prevent him from sealing in back into the breach each time?
Simply to put, yes, it seems that Firstborn just cycles his followers. As for the sumerian issue, who says it killed him permanently? It was still a surprise and it did destroy his brain enough to make him useless to stop Jericho.
Why was Delago the only one who figured out that the dreamless sleep was utter lie? Not only did the previous Jericho team members hold no secret that they were fighting a losing battle inside the pryxis, they also stated that dying there made you a monster. Yet nobody else but Delago actually questioned it. I understand Rawlings denying it, but guys like Black or Ross should have figured it out easily.
Because most of them probably didn't want to entertain the notion this truly was such an obvious suicide mission, or the eventual quasi-hopelessness of the whole endeavor. In the end they did the best they could really be expected to, but had some fairly frustrating blinders on the whole time which cost at least two of them their lives.
On a humorous note, why did nobody think of taping Litchhammer's mouth shut before they performed excorcism? Would have saved time.
She can spit acid. Probably wouldn't have done much good.
Did the Firstborn actually die or not?
In as much as something like the Firstborn can be said to "live" or "die", by the standards of humans? Yeah probably. He's not a human being so it's entirely possible that the very idea of his "life" or "death" is irrelevant...that being said he, in the end, clearly took on a form susceptible to mortality (instead of the immaterial, psychic entity he had previously been in the rest of the game, visible only to those with ESP) so it's likely whatever the living husk he was wearing was it was "dead". And if his mind was forced into it or stuck in it when he it died, he likely went with it. That was kind of the whole point, really, of the game, to force him into a PHYSICAL confrontation where he had to be at least kinda material and kill him.