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.
What is meta?
- Any Stack Exchange user can ask a question
- The community provides support, votes on ideas, and reports bugs
- Your voice helps shape the way Stack Exchange operates
Because we massively overworked Jeff as a matter of corporate policy, and because he wore big clown-like shoes, it will take at least three people to fill his shoes completely.
Josh "Shog9" Heyer, Stack Overflow user #811, has overall responsibility for Q&A quality and will be the public face of the company on metas. As such he's the closest we have to an "ultimate authority". Since he's usually right, I recommend listening to him.
Jarrod Dixon, Stack Overflow user #3, is now the lead of the core development team which works on the code that runs the Stack Exchange Q&A platform.
Jarrod reports to David Fullerton, the VP of Engineering for Stack Exchange. David's other responsibilities include the Careers 2.0 platform, Area 51 and the System Administration team (led by Kyle Brandt).
In addition, of course, there are many Stack Exchange employees who participate here actively.
As always, it's a community, and authority derives from you, our users, even if you're sometimes idiots and we have to overrule you.