Is there anything that makes you think that it can't be killed now? It's died successfully at least 6-7 times since release, though I don't think it's died for a week or more.
Keep in mind that it's designed as a cross server boss - many servers are supposed to bring a lot of their best players in order to defeat it - if 1-3 servers were able to kill it, then I feel like there'd be a bit of a problem.
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