[color=rgb(102, 102, 102)]Can you die in fallen London? Like forever? Losing everything and stuff?[/color]

No. Well, not at present. Normal death is temporary; once upon a time in the currently suspended Seeking Mr Eaten’s Name storyline there was a joke option to delete your character for 50 Fate. (Alexis, the lead dev, assumed nobody would take it so he never actually programmed in the deleting-your-character part. We know this because three people did choose it.)

I think at one point it was possible, from a narrative perspective. (The way I hear it, the player(s) did something that should DEFINITELY kill them, PERMANENTLY, and then submitted a bug report because the game didn’t do so - which I assume is also what Optimatum is referring to.)

But for the purposes of your question? Not really, no. :-)
My character has been exploded into little pieces at least twice, and I’m still kicking about The Flit just fine.