Re: Preventing a dojo coup
At our dojo there are plenty of dans and highly ranked students where there really isn't this issue. I don't know much of your situation or about ou dojo beyond what you've wrote, but entrusting a dan or highly ranked student with a key and permission to teach in his absence might help the dojo grow and stay cohesive.
I'm not one to just say jump up and leave your dojo. Schools aren't always easy to come by, especially schools with certified or competent sensei. Unless your sensei is lacking as a teacher or lacking in credentials I'd try to work it out. Aikido schools with competent instructors can die out from lack of students.