EDIT: To be perfectly clear, I'm aiming this question at the StackExchange 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 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.
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.