100%. Also, many players need new girls to keep them engaged and DPC is adding more and more and I bet he will keep doing that. This is one of the things that make the development take longer and longer, just look at the amount of new girls and scenes, it's crazy.
Let's just hope no Madame 2.0 is coming lol
There is no rule that stipulates that everyone must be involved to the end of the story (just the plot), but when that kind of thing happened (Mona or Cathy) it happened to every player.
As I said, you can make some unknown student fail and leave making the choice irrelevant, that's what you want? I think it's best to save it for later (when it can be meaningful) just like DPC is doing.
The fire was the start of the ending of AL, everything after that was just the final part (If I remember correctly with very little choice after the fire). But this is a way more complex and longer game and we're at chapter 9 of 16-20.
DPC can introduce another "fire choice" anytime but that's a completely different kind of choice, the 12? 14? you already made atm haven't changed the main story. They will at the right time. Since we're at the half of the story it's not the time to do that, you do that at the ending like every game developer does (and DPC did in AL, because unlike you he knows what he is doing) to avoid excessive branching. You can try to understand how it works or not, I don't care.