No one knows. She appears to be more or less supreme over Sigil, but has no power outside of it. She has killed one deity (essentially by the supreme magical version of backstabbing) that used to reside in Sigil. She hates it when people worship her or mock her. Given her actions in this game, it appears she just may have som appreciation for the Nameless One - ordinarily, you don’t get out of her Mazes, assuming she even gives you that chance.
Some theories hold that she is: Someone/thing close to being a deity, but doesn’t want to be (hence avoiding worship, which very well could make her a god); a supremely powerful spirit of Sigil itself; a dozen sqirrels with a mask, coatstand, robe, and a ring of flying (we’re pretty sure that last one is wrong…)
The phsyical world. Most DnD games revolve around this place. It a land of fantasy magic and so forth. The planes are vast but relatively unimportant. The Planes are the homes of the Gods and don’t really change much, whereas the Prime is always being fought over. Planescape turns this around and makes the Prime not very important (hence the mockery of the clueless Primes, like that guy in the Smoldering Corpse bar) while the Planes, especially Sigil, are where the action takes place.
The Baatezu and Tanar’ri hate each other. A lot. They’ve been trying to kill each other for eternity now and they aren’t backing down. One side will possibly win when the universe finally ends, or maybe neither will ever win. Or maybe one side will win and that will end the multiverse as we know it.
According to one source, Asmodeus, lord of the Baatezu, is the ultimate champion of Law and Evil, and seeks to remake the universe in the image of Baator. Maybe the Blood War is part of his plans or it may be a legend.
Sort of. Its theoretically possible for it to just end and both sides stop fighting. But that probably won’t happen. Its sort of become a fixture of the Planes.
Who knows? Sadly, Interplay basically went out and spent the last three years gutting Black Isle and screwing them over, and then finally fired nearly everyone in it. They have the Planescape rights and they will surely ifgnore it. ANd if they didn’t, they’d turn it into a Dark Alliance-type game. Black Isle was one of the last good divisions left at Interplay, and now they’ve tortured it to death. Very sad.
Not long before they got canned, Feargus made some noise about going back to do another Planescape game. Probably not the NO’s story, but in the same vein.