There will be many causes for Wikileaks' death (if in fact it does in fact die). None more damaging though than the damage Wikileaks did to itself. Leaving unredacted the names of informants who were later executed for providing the very information Wikileaks posted clinched its fate IMO.
I stand corrected. There's no proof any source has been killed, but the Taliban has repeatedly vowed to hunt down and "punish" the sources not redacted in the Wikileaks docs. Many links on that on the Web.