So during Todd Howard's presentation, he mentioned that you (the player character) are in Vault 111 for 200 years, then you're the "Sole Survivor", i.e everyone else dies, and you leave. What could have happened that wiped out everyone but you?

A few possibilities:

1) If indeed you're cryogenically frozen/artificially preserved (like House was), perhaps a malfunction occured, and by chance your pod or whatever was spared.

2) An attack from the outside. Since the Vaults can be opened from the outside (although only if opened from inside or with a code), maybe an outisde force managed to get in and attack the Vault. Maybe a breach from underground, even. Likely culprits could be Raider, Super Mutants, maybe even the Brotherhood of Steel.

3) Civil War/Mutiny. Maybe some sinister experiment is going on in the Vault, and just like Vault 11 there was a civil war which only you survive.

That's all I've got.

Your character died as well.

You spend the game trying to get your wife and child's memories and personalities installed in an android. Towards the end of the game you learn that you died like everyone else and that your memories have been transported into an android.

It could be that the vault experiment was for the vault to unlock after a certain period of time (200 years) and then force its citizens out in to the wastes. However, the Cryo pods could have malfunctioned, a riot in the vault, people being killed by the vault systems for refusing to leave etc.

An attack, or decease, of some sorts does make sense. And cryogenic sleep is really the only option to stay alive for 200 years.

Either you were frozen or you're an android with fake memories.

I really hope you're not an android in some plot twist

Either the preservation method failed for everyone else, or everyone else melted from post-cryogenic syndrome.

I hypothesized something like this. It's admittedly crazy and highly implausible, but I kind of like coming up with stuff like that. Blame it on all the time I spent on the TES Lore Forum.

The vault experiment was to preserve physical and mental data of its participants in a database, and then compare it to the subjects when they emerge from cryosleep, to learn the long-term physical and mental effects of being cryopreserved. The Institute uploads the data into an advanced android (specially modified to look like the vault subject) to perform an experiment of their own, to see how an android with pre-war memories will adapt in the post-war Commonwealth. Eventually they'll come for you, intending to extract all the data out of you.

If we adhere to actual lore and observe the fact that advanced cryotech was not perfected prior to the Bombs, we all but have to conclude that 111 must have been an experimental cryo vault with an anomaly.

Then there is the questioning of using such an unperfected measure for the life support of the upper echelon of the population.

My GUESS is that they were experimenting on cryogenic systems and you volunteered to be a test subject with the test only suppost to a month or a year, but something happened and you are not woken up because everyone in the vault is dead. You get woken up 200 years later. Why? Maybe the event that killed everyone had a lingering danger to you like posion or radiation and it only disipated after 200 years. Maybe the systems ran out of power and they have a failsafe to wake you up if they lose power.

Well back a few years ago i wrote a basic script for a fallout, never did anything with it just for imagination and fun. Anyways but in the story people are cryogenically frozen but one of them betrays the rest and gets them all killed. So i think maybe some sort of foul played outside of the normal vault-tec bs.

I have my doubts about the whole "You are an android twist at the end".

It just wouldn't work for me, I mean, you see doctors when you're injured, you bleed, your bones break and fracture. Surely someone would have noticed you are an Android.

The Vault is sealed, no androids prewar. I think the vault was broken into.

I think our character is a android. I don't understand why they would open the vault with so much radiation around just to let one you guys in.

Yea, I don't know how they would get around this--as well as whatever anatomically revealing death sequences your character can suffer--and still have the "surprise, you're an android" ending.

I'M going with Rad Roaches.

Radiation leak weird medical procedure.... Universe is holotape

My guess is that your family will have survived with you and will have left the Vault some time ago, at least enough so that your son is an annoying child rather than baby, if not an advlt you meet along the way.

There is a post war weapon in the inventory of the player during the E3 Showcase, so I'd assume your awoken from your time as a popsicle because someone (probably raiders) is looting the vault and you have to escape the Vault as they have killed off everybody else in Cryo.....and then the intial focus of the main story is finding your family.

You get the Pipboy off of the skeleton of a long dead Vault 111 scientist. I'm guessing by the fact he died in his labcoat, his position on the floor, and the fact he wasn't buried, means something must have gone terribly wrong in the vault..

I've read about this (and taken part in some) argument a lot on other threads.....

So basically the Vault main door at the bottom of the shaft is probably still open when the family are at the shaft entrance since there is a scientist (who maybe the skeleton you get the pip buy off), a Vault security guy and a guy in Power Armour escorting the civilians into the facility. Logic says they would have probably sealed the Vault, but we know from Bethesda that they do at least let the protagonist in.