Alas
Explorer
That's definitely something the players should discuss going in. Can your characters die on this expedition? If they do, do you promote a porter to PC, or is the expedition over for them? Failing is certainly not the outcome the players are looking for, but I think a game should have some risks. I guess a good question would be, how do I arrange the game so that the players still get something out of the expedition failing? Adventurers who don't come back do pass into legend, sometimes...The biggest downside to this would be that a serious fail state, historically, meant that the people on the expedition died. Not something players like to experience.