In a truly unfair world, one that merely 'was what it was', such reliable information wouldn't necessarily exist. PC's could stumble into certain death despite their best and most diligent efforts, occasionally random, inescapable dooms would sweep, tsunami-like, across these dangerous worlds --be they in the form of a horde of undead, rampaging giants, an elder wyrm having a bad day and an uncharacteristic fit of pique, or even an actually tsunamis, if the PC's are on the coast.
I've always thought something of the sort would be a great way to start a campaign. It is a far more realistic beginning to a campaign than, "You all meet in a bar, and decide to trust each other with your lives despite your different backgrounds, then immediately decide to follow up on a rumor of a dangerous dungeon containing a treasure." Instead, the party would be thrown together as strangers by larger circumstances, and like so often happens on such occassions, would find themselves relying on strangers for their very survival.
If you look at real world disasters, they almost are never invariably lethal. Most real world disasters, even the most dramatic and large scale ones, might just kill 10% or 30% of the population. Not everyone died at Pompeii. Some of them said, "That looks bad, I'm getting out of town." Not everyone died when Krakataoa blew its top. Some of them made it to high ground. I would have no particular problem starting a campaign with a tsunami, an attack by an elder wyrm, or a horde of rampaging giants. That would be a very fun start to a campaign I think. It would provide the sort of immediate action that helps jump start a campaign and get everyone's attention. It would be a very nice hook. And, because it would be occurring first thing, the players almost certainly wouldn't be confused into thinking that the event is personal to them and requires dramatic on their part other than surviving.
There would to me be nothing particularly unfair about such a campaign start, because I've already stacked the deck in the PC's favor by allowing them to play a character with greater than average starting resources and abilities. If the event is going to kill say, 30% of the population, then they are very likely to be in the 70% of survivors. What would be unfair is staging such an event and having it be all about the PC's, as if they were the center of the universe and everything revolved around them. Sure, if the elder wyrm decided to target the PC's specifically, out of a population of 10,000 city dwellers, they wouldn't stand much of a chance. Similarly, if the tsunamii had been aimed by some hostile power (like the DM) specifically to drown the PC's, then they probably wouldn't stand a chance. But, if I treat them as mere average members of the city, then the elder wyrm will probably pay them no particular heed and the challenge the PC's will face will be much closer to the challenge most everyone else in the city faces - a challenge most of them will succeed at too.
If I ran such a game, I would probably ask everyone to start with two characters, just to ensure that no one would get put out of play in the first few minutes and be forced to watch (unfortunates that lost both characters could take one from someone with two), but since I've done that before, it wouldn't represent a dramatic departure from my normal low level play at least in that regard.
Sure, it's not possible for me to be perfectly unbiased in running such a scenario. I'm human. I don't have the ability or desire to run a simulation of 10,000 fleeing NPC's, so what the NPC's do is going to in fact be scripted rather than simulated. Not so for the PC's. I won't really have the slightest idea what they'll decide to do, and I'll probably only have some vague ideas about what they'll actually do to survive. They'll probably end up surprising me by doing something I never really considered.
