Perhaps Kel'thuzad deceived Arthas in regards to Sunwell.

[Dark Succ]

Kel'thuzad is the Patron Saint of All Necromancers, the title being only contested by Ner'zhul and Arthas themselves, so the fact that he didn't use his infamous phylactery to ressurect himself, instead telling Arthas that he needed to go all the fucking way to Isle of Quel'danas to ressurect him seems odd to me.

Sure, Kel'thuzad was powerful, yes, but not that powerful. He wasn't a Medivh for fuck's sake. Well, not at the time. (KEL'THUZAD'S SECOND DEATH IS ALSO A SETBACK, THAT MOTHERFUCKER IS JUST TOO FUCKING AWESOME AND CRAFTY TO DIE) Perhaps he sought to increase his own considerable power via the Sunwell, or defiling it was the primary goal in the eyes of the Lich King, and Kel'thuzad's increased power & return to the ranks of the damned was actually a side bonus, or Kel'thuzad wasn't meant to survive, yet came back due to having manipulated Arthas to ressurect him with Sunwell's power.

I love the headcanon of Kel'thuzad pulling a subtle fast one on Arthas and Ner'zhul re-evaluating his lieutenant and thinking "Well played, you magnificent son of a bitch."

[Al Gorefiend]

I think he needed a powerful font of magic to resurrect. I hope we see more of him in Maldraxxus, it’s probably where he was chilling in between resses and perhaps currently is now.

[formerShandalay]

His first death was his 'mortal' death, he was still actually alive when he got killed by Arthas. The Sunwell was used to turn him into a powerful Lich.
He had a phylactery only afterwards.
The thing is, he was a human that was brought back into undeath and made a Lich with the whole power of the Sunwell. If you look at other Liches, who are powerful too, they get made a Lich just by some magic (powerful magic, but not the freaking Sunwell).
So yes, this Lich is special and super-powerful, a lot more than other Liches. But he didn't have a phylactery when the Sunwell was used, because he was no Lich before that, just a necromancer.

[Calfredd]

I think he needed a powerful font of magic to resurrect. I hope we see more of him in Maldraxxus, it’s probably where he was chilling in between resses and perhaps currently is now.

Except I'm under the assumption that the soul resides in the phylactery until it is destroyed so I don't think he'll be in the Shadowlands unless Blizzard said he died for good back in Wrath.

[Caerule]

Second reply of the thread is correct.

Kel'thuzad was still mortal when he died. He only became a Lich through the power of the Sunwell.

[How dare you]

Kel'thuzad is the Patron Saint of All Necromancers, the title being only contested by Ner'zhul and Arthas themselves, so the fact that he didn't use his infamous phylactery to ressurect himself, instead telling Arthas that he needed to go all the fucking way to Isle of Quel'danas to ressurect him seems odd to me.

Sure, Kel'thuzad was powerful, yes, but not that powerful. He wasn't a Medivh for fuck's sake. Well, not at the time. (KEL'THUZAD'S SECOND DEATH IS ALSO A SETBACK, THAT MOTHERFUCKER IS JUST TOO FUCKING AWESOME AND CRAFTY TO DIE) Perhaps he sought to increase his own considerable power via the Sunwell, or defiling it was the primary goal in the eyes of the Lich King, and Kel'thuzad's increased power & return to the ranks of the damned was actually a side bonus, or Kel'thuzad wasn't meant to survive, yet came back due to having manipulated Arthas to ressurect him with Sunwell's power.

I love the headcanon of Kel'thuzad pulling a subtle fast one on Arthas and Ner'zhul re-evaluating his lieutenant and thinking "Well played, you magnificent son of a bitch."

They probably had not thought of the phylactery thing all the way in WC3 and they just wanted to have a cool mission.

[rated]

Second reply of this thread pretty much ends the thread.

[Trumpcat]

I've been thinking Kel'thuzad might show up and somehow restore the original Lich King or become it himself, but now with the recent developments in Icecrown... I do still hope we see him return gloriously, however with how recent grand villains have been treated even if he does show up all he'd do is speak some evil lines and die within the same raid tier. Might have a cutscene if lucky.

[Destinas]

I think he needed a powerful font of magic to resurrect. I hope we see more of him in Maldraxxus, it’s probably where he was chilling in between resses and perhaps currently is now.

A Lich's Phylactery is nearly exactly like a Warlock's Soulstone. It prevents the soul from passing on to the Shadowlands, so they can revive in the world of the living.

Kel'thuzad's Phylactery was never recovered in the Northrend version of Naxxramas, and it was never destroyed. So, if anything, he's just chilling in there. But, he wouldn't be in the Shadowlands.

[Ulthane]

Oh... he never died, he did in fact resurrect but didnt show his face after. We never found his Phylactery a 2nd time.