Seems like most MMO's have had a procedure in place for these situations, you just had to put in a support ticket. Have you tried that?
I mean, if they say they can't help you, then it seems like you're just SOL for their oversight.
I can't say this is the most helpful thread I've ever seen.
Here's what they have to say in the ESO Customer Support knowledge base:
"What can we do if our guild leader disappears?
If the leader of a guild has become inactive for an extended period of time, guild members should contact Customer Support for assistance.
Date Updated: 05/17/2014 "
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