How will returning to your PhD advisor as a post-doc affect future career options in academia?
It really depends on what country you are working, and what are your final goals. Most European academic institutions do tend to hire for tenure people who got their PhD in the same institution. I personally believe it is indeed an insular, unwritten policy, that is detrimental for professional development, and impoverishes the institutions research. Contrarily, most USA institutions take for granted your willingness to explore beyond your comfort zone. 
As far as it concerns you personally, you see where I am heading by the language I am using :)