Hmm I want more info on this. Where did you hear it? If the story isn't effected much by any of the decisions you make up until what you're saying that's pretty bad. My whole interest is to alter little things possibly going down different paths. Choosing not to go in private property T-2 without a warrant to avoid being benched if I'm caught, missing out on possibly great chances to work on the case and finding the killer for example. I believe screwing up on finding enough evidence, and clues are in this though. One reviewer talks about false evidence. I guess I really have to wait for Wednesday to ask people that played the game.
About the spoiler, she seem like a important character, I suppose she can't totally not show up. Well did the guy playing try pissing her off, and walking out after using the inhaler not helping her with the guy at all?
Edit: Actually things are showing good promise on having a different path in the demo. I got a good range of different results that in it's own way effected the story. Piss her off and don't get her to talk to you. Leave her to get beat up, don't ask if that's her son on the dresser resulting in her not crying and you not trying to comfort her having her to snap at you, and other things you can skip or miss.
Maybe your collected effort in solving the crime pays off in that quarter you're talking about. Depending on how you do + if you keep the needed people alive that are key to whatever is going on, the story could greatly change at those points. However having the other things you do before is pretty much filling up a evidence/case/sanity meter to determine if you'll be successful in catching the killer. Each play could still be a different story as seen with the demo of 2 scenes. Maybe the worse you do the more injured, drugged, freaked out, and crazy your characters become. It could really look like they are struggling to make it through, with bruises, shaking drug fending, and other visible things to go along with it (snake's last stretch of mgs4 for example).
A few more days for everything to be straightened out though. Your info could be very right and it could still fit with what they were saying so it's not a total deception. If all characters die the game winds down sooner for the player, but the story continues. The loss of people will effect you because all of the work you put into helping them get through with their information could be just like they described.