cbw - no responses yet? I have to be careful. I'm new to the boards (but not PTO work)and am quickly becoming addicted!!! This is a great place to meet helpful people and learn a lot...
Maybe the principal isn't thrilled with the direction (or lack of) that the original officers were going with the PTO and wants to be in charge of regrouping things. Keep the lines of communication open and work together to help the PTO evolve into an entity that fits well with the school's vision.
Regarding your question
who is going to be the ultimate authority of the PTO next year?
Even with a full PTO board in place, your principal is the ultimate authority as that is the first person disgruntled parents, teachers and BOE members call. Also, the principal sees the big picture and can help a parent group fit within the framework.
For our group, the officers seek out folks for the board positions (officers and chairmen) and the principal recruits the two teacher reps.
To move forward? Meet with the principal. Be open minded and flexible but also have a plan to share. Be patient. Maybe you won't have a full board this year with bylaws and the works. But with the principal, 2 teachers and a handful of trusted volunteers in place you can begin to set some solid groundwork. If you do it right from the beginning, members will thank you for many years to come!