My opinion is that rather than defeating the Khazars and forming a link with the byzantines, the Rus' states focus more on political and cultural consolidation and development.
The problem with this is isolated Rus would just be one of dozens ethnic groups in Modern Russia. They would just be minor pagan tribe like Mordvin.
Successful Nation need many things : trade deal with surrounding people, victory in war against surrounding people, cultural achievement to attract member of surrounding tribes to join. Rus nation itself born to maintain Baltic-Black sea trade route and resist Khazar custom duties.
Isolated Rus would be dislodged from this lucrative trade route, they would be target by surrounding monotheistic tribes, and their citizens would desert to join richer people.