Doomblade, can you be a little more specific? There are a number of paths you could take to try to sneak around them.
Does an undead have to have every piece intact to be re-reanimated?
No, or else skeletons would already be missing too much for skeletal undead to even be a thing. Plus, Skeletal Constructs and such would be an impossibility.
How does shadow bolt effect undead, reducing the HP of the head actually destroy it, or just un-animate it?
It would destroy it.
Does blind have any effect on a melee user?
Yes, unless they're Daredevil or something. Melee isn't just waving a sword around in a random direction. Though, if someone is waving a sword around right next to you, it's pretty likely they'll hit you anyways.
If an undead permanently raised with a crystal is defeated, then raised again, does it require another crystal?
I'm guessing you mean raised with EP? Arcanite Crystals are just concentrated amounts of EP that crystallized.
If that's what you mean, then of course. It couldn't be defeated without being defeated, if that makes any sense at all.
If that's not what you're talking about, then I have no clue what you're talking about. Crystals don't have anything to do with this.
Are there spells to reap souls?
That'd only really be possible as a god/demigod, but even then only 'technically'
Is it possible to find or create a weapon enchanted to reap souls?
Perhaps if it were created by a God.
Could souls be used as a substitute for arcanite power, if properly tapped?
No. You can of course use them to create intelligent undead, but of course they'll only be willing to follow/assist you if they were willing to before they were dead.
Did any actual gods exist when I was still fleshy? Were they rather active?
Of course.
Who is the most infamous necromancer/evil god/abomination from beyond space and time, that I can remember?
You don't know their names, or if they even had names. You just know they were a part of E.V.I.L.
Do I, by some unholy miracle, still have a beard?
Dwarvern beards work in mysterious ways.