Logan's research

What would have happened, if the chosen undead never encountered Logan at the top of the archives? if we didn't have to kill him, would he become the new Seath? by this i mean rule over the chanellers, the serpent men and such

Because he obviously mastered som of Seath's magic, and has access to all of his knowledge, nothing keeps him from taking over

He turns himself into a dragon, only to realize that it handles completely differently from his old body; attempting to leave the room, he faceplants on the first step, impaling himself on the crystalline spikes.

He bleeds out a few minutes later.

Nobody gets a happy ending in Dark Souls.

Yeah that sounds like it could happen ^^.

Logan's main agenda is to pursue his quest for knowledge and whilst he undoubtedly manages this to an extent the Archives is a very dangerous place to do such a thing. I still think he would have lost his mind there regardless.

On a serious note, it is possible that Logan would have taken his research to the extreme by kidnapping innocent people and crystalize them, much like Seath did.

Though seeing how batshit insane he became, I would consider him rather harmless, unless somebody was to enter his domain.

I must say, though I do not approve of Seath's meddling, I do like his crystal weapons! Wonderful profit for my little traveling store!

I think he would get killed by a Man-Serpent or something; I mean, he's running around stark naked and he isn't doing a Naked Boxer Challenge, so he wouldn't fair well.