Or maybe Shinichi will appear to be dead (at least to everyone and even the audience) to only later make a huge unexpected and surprising comeback. That's definitely a path I could see Aoyama take.
It's clear that so far, he's been great at surprising us with lots of little twists and unexpected events. Therefore, I wouldn't be surprised to be surprised until the very end!
Regarding the boss, there are so many theories indeed. Once again, knowing Aoyama, it'll most likely end up being someone we don't expect at all. Maybe we should keep track of a list of "potential" characters that could fit the role? (even in the craziest way lol)