Teron Gorefiend, I am - questline

Hello Warmane community.
I came here to seek help for the latest problem I ran into. As the title says, I've been doing the "A Ghost in the Machine - Teron Gorefiend, I am" questline in order to get my twink a headpiece.
I ran into a problem when I've been doing the last quest of this questline, "Teron Gorefiend, I am". It started off well, Teron possessed my character, been fighting Karsius for a while and when I actually killed him I got no credit for the quest, like I never fought him. The quest continued, Teron mounted up, said his lines, and when he was supposed to leave it didn't, I got bugged in "Teron form" and I couldn't leave it. Eventually, after a couple of minutes, I dismounted and I still didn't have the quest completed. Ever since then, Teron is walking in 1 spot, http://i.imgur.com/wTIEJvf.jpg and not disappearing and the NPC that gives the quest isn't spawning at all, its been like this for at least 30 minutes and I'm still waiting over there.
I have abandoned this last quest, hoping for npc to respawn so I can take it again and do it all over again.

So, does anyone have a clue what's going on in here? Can anyone help me out? Do I, perhaps, have to wait longer for the NPC to respawn? Is this quest, last quest, bugged or something? Did anyone complete it before/after the new core was implemented of Deathwing/Ragnaros?