To be perfectly clear, I'm aiming this question at the Stack Exchange management, who will be (presumably) filling the void left by Jeff with other team members.
Because we massively overworked Jeff as a matter of corporate policy, and because he wore big clown-like shoes, it took at least three people to fill his shoes completely.
Josh "Shog9" Heyer, Stack Overflow user #811, had overall responsibility for Q&A quality and community management, and became the public face of the company on meta sites. As such, he was the closest we had to an "ultimate authority" when it came to community-related decisions.
Jarrod Dixon, Stack Overflow user #3, became the lead of the core development team which works on the code that runs the Stack Exchange Q&A platform.
Jarrod reported to David Fullerton, the VP of Engineering for Stack Exchange. David's other responsibilities included the Careers 2.0 platform, Area 51 and the System Administration team (then led by Kyle Brandt).
None of the above employees still work for Stack Exchange today, but these were the ones who directly replaced Jeff at the time he left.
As always, it's a community, and authority derives from you, our users, even if we sometimes have to overrule you.