Shrine of the Truthguard

After receiving the Artifact, I simply hearthed to Dalaran. This left the quest requirement for returning to Dalaran incomplete. I was able to complete it by getting back on the hippogryph and returning to the island, then immediately getting on the hippogryph once I got there to return to Dalaran.

The dwarf and hippogryph were not in Dalaran when I first arrived there. Relogging caused them to reappear.

P.S. I personally was unimpressed by Cato's much-vaunted healing abilities. I would prefer to have waited in a queue for a better healer.

You must return to Dalaran to complete the quest requirements. However the actual quest turn in is to Lord Maxwell Tyrosus in the Sanctum of Light.

I had a fair bit of trouble with this when I did the usual "Run in and hope nothing kills me" bit. Specifically at the tomb.

Once you're inside, there are three guards and a bunch of orb things. First thing, make sure you have [spell=20066]. Use this on the larger of the three guards. I used the [spell=203776] talent as well to avoid breaking CC with the shield.

Drop consecration to kill the orbs and single target the other two guards. Once everything but the big guy is dead, heal up and kill him. [spell=204019] may prove useful also here if you can avoid breaking the CC. [spell=204054] may also help kite the orbs. Hammer of Justice as needed.

Once they are down, use Divine Steed to charge towards the end of the hallway, avoiding whirlwinds. Once you're up the end, LoS pull the casters one by one into the stairwell to clear the wind.

Once all is clear you'll be able to attempt to open the door. Use a tanking cooldown to survive the damage the door does to you and you'll meet Yrgrim the Truthseeker and [npc=106172].

[spell=20066] [npc=106172] so that you can focus on Yrgrim the Truthseeker. Use Hammer of Justice to stop [spell=191884] or [spell=128750] as needed. Your NPC buddies will help with this as well, although they are more likely to simply stun him on cooldown rather than when he needs it. As long as you keep healing up with [spell=184092] you should be able to take care of him easily enough.

Once Yrgrim the Truthseeker is dead, he will start a scripted encounter and you'll be able to pick up your reward. Don't do this until you've beaten [npc=106172] as your NPC buddies will leave as soon as you have [item=128866]. The main thing to note is to interrupt when she casts the ability which shoots ice shards with knockback.