Here's an interesting question from Thomas Deathgem:
what did malistaire do with bartleby's eye of the past?
He stole it.
Yeah, that one is kind of a mystery isn't it? I'm not sure if that was ever fully clarified in any quest text out there. What the heck happened to Bartleby's eye of the past? Why did Malistaire steal it?
Let me go out on a limb and see if I can come up with a possible conspiracy theory. How about that? Let's get a little wacky crazy, kids. WOOT!
If you look deeper into Malistaire's chain of events leading up to the awakening of the Dragon Titan, you'll see some complex things happening. Malistaire was hunting for the Kroknomicon and found it eventually in Marleybone. The Kroknomicon was the most powerful source of information about Life and Death Magic. His intent was to use it and a few other artifacts to bring the power of the Dragon Titan back to the spiral since he was under the impression its power would help him bring his wife back to life.
Now, digging back into the lore of the game we find that it was Bartleby who not only created all the big bad original creatures in the spiral (aka the Tritons, Dragons, and Giants) but it was also him who sung them to sleep and created the spiral as we know it with the help of the Great Raven and some pretty long root systems of his own.
Stealing the Eye of the Past seems important because either it would help him discover the hidden location of the Kroknomicon OR it would cloud Bartleby's mind of the past. In fact, talking about the past with Bartleby seems to just make him extremely sleepy.

You see, Malistaire couldn't have Bartleby messing things up with his dragon titan that he was summoning, so he needed Bartleby to forget . . . to forget how to sing them back to sleep . . . OR, maybe to teach himself how to sing the dragon titan to sleep after it had been used for his purposes.
We never find this eye after defeating Malistaire. It's a hole in the story. Here's some possible theories:
1- Malistaire took it with him when he was killed . . . I mean "defeated" . . . by you. Now it's residing with Malistaire in ghost mode.
2- The book, the eye, and everything else was "used" in bringing the Dragon Titan back to life. Much like you "use" a crafting reagent to create something new, perhaps Malistaire was "crafting" a spell to bring Sylvia back to life and so . . . it's gone, consumed, goodbye eye of Bartleby.
3- He stashed it somewhere. Maybe in some later quest we'll find it because the eye is once again needed. So we'll have to follow the clues to get the missing eye of Bartleby back.
4- Bartleby is better off without it.
WHOA FRIENDLY, WHOA!
Ok, let me expound on that a little bit and see if you can follow this bit of philosophy I'm gonna drop here. So, Bartleby appears to be named after a character in Herman Melville's less popular work:
Bartleby the Scriviner. Yeah, the Moby Dick guy wrote another book. In fact, some consider it a work of genius. They've tried to adapt it to film a couple of times.
I'm not going to restate what wikipedia says about the book or the countless other sites out there that dissect the book into all its myriad pieces and nuances. But I will tell you this. The metaphor of a tree is a perfect one for an unmovable character such as Bartleby, the Scrivener. By the end of the book, our anti-hero is completely nuts and does nothing much but refuse to do anything.
Now, take a look at our Bartleby. In a way, he is a very sad character. Imagine bringing life to a world and having that life do nothing but war and bust the land apart . . . and all the marvelous things you have created must be put to sleep at your own hands.
Bartleby, the Scrivener basically went insane from not only the horrible realities of lost hope from working the Dead Letter circuit, but perhaps because he could not let go of the past and find hope in the future.
For our Bartleby to be a more hopeful character, mabye it was best that he forget the past and only look to the future.
The power to make amends, forgive yourself, and forget your past mistakes is a huge boon to all of our mental health.
Maybe Malistaire did him a favor.
...
dot dot dot
SO, Thomas Deathgem, my answer is . . . he stole it. The rest is possibly deeper character development, a quest for the future, or something to remain shrouded in secrecy for the rest of your life. MUHAHAHA!
Or maybe my readers have conspiracy theories of their own (share please!).
Happy Dueling!