I can guarantee you Aion will NOT be the death of WoW, not even close.
Remember Age of Conan? How it was supposed to kill WoW, look now? Didn't even touch WoW's userbase.
Remember Warhammer Online? It was supposed to kill WoW.. Warhammer's servers are next to dead now.
Aion will not "kill" WoW. From the looks (and the beta play) it brought absolutely nothing new to the table that another MMORPG hasn't already done.. Wow! You can have wings! MU Online did that, Wow! You can fly.. Fly for Fun did that.
PvP? Nothing new, it's based on RvR (realm vs realm), what game did that already? Dark Age of Camelot.
Game gets awfully boring after a while, and it won't kill WoW for one reason. Aion is too graphically made, people wan't games that they can play enjoyably on. WoW is playable on a VAST variety of computers, Aion you will have like 5fps if you don't meet the requirements.
Blizzard wins with their games because they don't push the graphics to the max, that's why all of their PC games do so well.
Aion won't touch WoW's 11M+ Subscribers, ever.
Guaranteed.
Edit: When Aion sells 2.8M copies in the 24 hours like World of Warcraft: Wrath of the Lich King did, then we can talk about "death of WoW".