Very well put. Life rarely goes to plan, and no one really knows what will happen. The bittersweet conclusion doesn't force a happy ending or a tragic one, but one of uncertainty and room for the unknown. It's easy to long for unrealistic stories because stories themselves are often used to escape from the brutality of the real world.
Major Spoilers:
That's the moral of In Case of Emergency. Peregrine seduces the characters with its promises of adventure and freedom, but in reality, it's a shackle holding them to a false world. Escapism can be enticing to those who need it most, but it's never as pure as it makes itself out to be. In the end, they all realize that it's foolish to abandon reality for superficial happiness.
You never know what happens to the characters, just as you never know what tomorrow may bring. I've played through every path, every story in this game. There's a sort of peace at the end of each so-called "good ending". Although we will never know what becomes of Luke, Cedric, Wesley, Remus, or Kieran, it's a pleasant thought that maybe, just maybe, things will be alright.
Like you said, life will always have many differing paths and conclusions. Not everything will end in happiness or love, and more times than not, it won't. It would be naive of me to see the world in black and white. Remus was not evil for doing what he did, nor was he a savior or hero of any sort. He was a complicated old man who lived a life of fantasy for so long that he had forgotten the truth.
All of them learn different life lessons at the end of their paths. Wesley realizes that he can't keep living his life for others, not allowing himself to make any decisions for himself or be free. Cedric learns to let go of all the ideals and meanings he tries to force himself to conform to. Luke discovers that not everything in life will have a solution or some sort of magic to repair it. Sometimes you just have to go with things and live in the moment.
Anyway, I know I probably seem insane for taking the time to write this much, but I enjoy to have discussions like this with people. Some of the best conversations to be had are with those you'll most likely never see or know. Thank you for taking the time to read this, your willingness to converse with people in such detail is admirable.