Al Qaeda has acknowledged on its websites that Bin Laden is dead. So, will that deal a, ahem, deathblow to the Deathers who deny that the US killed Bin Laden? Probably not so much as Truthers never took Bin Laden and folks at their word. Conspiracy theories do not die, because the zealots who buy into them are very good at ignoring reality. Always easier to hold onto a belief than try to fit uncomfortable bits of reality into one's world view.
So, just as Obama's long-form birth certificate only convinced some folks, AQ statements about the death of Bin Laden may not be bought by the Deathers. Still, for those who can be persuaded, this acknowledgment is significant. Confirmation is not a bad thing at all. I just wanted to point out that it will not convince everyone.