A few more questions, mostly minor, one major:
1. What was Vin _supposed_ to do at the end of WoA? How exactly did not-using the power, end up releasing Ruin? I still don't get how that all worked. Can you explain it?
Minor q's:
2. If Sazed is the HoA, then who is the Announcer?
3. Allomancy is fueled by Preservation's body? How exactly does that work? And how does that interact with Atium -- it's fueled by _both_ gods' bodies?
4. Why exactly do some spike removals kill (dual eye, or central spike) but most don't?
5. Did Zane get spiked intentionally? Did someone else (Straff?) know about hemalurgy?
6. Very minor question -- was Reen a misting or mistborn, and if so, did he end up as a spike in an inquisitor somewhere?
1. What was she supposed to do? Well, this is difficult to answer, since the prophesies have been changed and shifted so much. Originally, the prophesies intended for a person to go take the power every thousand years and become a protector of mankind for a period of time. Someone to keep an eye on Ruin in Preservation's absence and watch over the world as he would have done. Imagine an avatar who arrives every thousand years and lives for their lifetime blessing the people with the power of Preservation, renewing Ruin's prison, and generally being a force for protection. (Note that Ruin wouldn't have gotten out if the prison wasn't renewed, he'd simply have been able to touch the world a little bit more.) Obviously, it changed a LOT during the years that Ruin was playing with things.
What should she have done? Well, Ruin's release was inevitable. Even if she hadn't let him go, the world would have 'wound down' eventually. The ashfalls would have grown worse over the centuries, and the next buildup of the Well might not have come in time for them to do anything. Or, perhaps, mankind would have found a way to adapt. But Ruin was going to get himself out eventually, so the choice Vin made was all right. There weren't really any good choices at this point. She could have decided to take the power and become a 'good' Lord Ruler, trying to keep the world from falling apart. Of course, she would have had to make herself immortal with Hemalurgy to make that work right. And since she was already tainted, chances are good she wouldn't have ended up any better than the Lord Ruler himself.
2. The Announcer was a fabrication of Ruin intended to reinforce the person HE wanted to be the Hero.
3. The powers of Ruin and Preservation are Shards of Adonalsium, pieces of the power of creation itself. Allomancy, Hemalurgy, Feruchemy are manifestations of this power in mortal form, the ability to touch the powers of creation and use them. These metallic powers are how people's physical forms interpret the use of the Shard, though it's not the only possible way they could be interpreted or used. It's what the genetics and Realmatic interactions of Scadrial allow for, and has to do with the Spiritual, the Cognitive, and the Physical Realms.
Condensed 'essence' of these godly powers can act as super-fuel for Allomancy, Feruchemy, or really any of the powers. The form of that super fuel is important. In liquid form it's most potent, in gas form it's able to fuel Allomancy as if working as a metal. In physical form it is rigid and does one specific thing. In the case of atium, it allows sight into the future. In the case of concentrated Preservation, it gives one a permanent connection to the mists and the powers of creation. (I.e., it makes them an Allomancer.)
So when a person is burning metals, they aren't using Preservation's body as a fuel so to speak--though they are tapping into the powers of creation just slightly. When Vin burns the mists, however, she'd doing just that--using the essence of Preservation, the Shard of Adonalsium itself--to fuel Allomancy. Doing this, however, rips 'troughs' through her body. It's like forcing far too much pressure through a very small, fragile hose. That much power eventually vaporizes the corporeal host, which is acting as the block and forcing the power into a single type of conduit (Allomancy) and frees it to be more expansive.
4. For the same reason that a bullet through one part of the body will kill you, but getting shot somewhere else won't. The physical form of a person who has undergone a Hemalurgic transformation is no longer what we think of it. The direct connection to Preservation starts keeping them alive. (Imagine stapling someone's soul to another person's soul, their life essence, then stapling that to the power of creation itself, giving you a conduit directly to power, letting you leech it and steal it.) That power keeps you alive, despite the wounds. Some of the time, the other staples are enough to keep you alive, even if one is pulled out. Others are too important.
5. Zane spiked himself. It was...a very twisted and messy process. Note that Ruin tries to get Spook to do something similar. It's much easier for him to work with someone to get them to spike themselves than it is to arrange the exact circumstances where someone gets spiked.
6. Reen had no Allomantic powers, I'm afraid. His father was skaa. (He was Vin's half-brother, if you recall.) And yes, he is dead.
