I really don't see why Saul would come back into the CIA in any type of lesser position, the only thing that made somewhat sense in the finale was that Saul did not stay in the CIA. Lockhart simply could not keep him on, you can never keep on a guy who once sat in the big chair. Now, why Saul had to be forced into retirement rather than being promoted up to an even senior position like Director of National Intelligence or National Security Advisor beats me, but if he comes back working under Carrie then things will just be beyond stupid.
Second, how are they gonna have a show where Carrie is the Station Chief? Do they know what a Station Chief does? Carrie would be responsible for all intelligence operations and the operatives in that country, she'd essentially be what Saul was. You know what that means? It means she can't be running off in the field doing shit, she has to sit behind a desk and order other people to do stuff. Also, can you imagine a worse boss that the mentally unstable Carrie, jeez I feel sorry for her subordinates already.
The writers probably thought of a really great Istanbul unstable pun and decided to go for it.