As a result, classes have lost some of their energy and flow, and I don't feel like I am getting the most out of my training. So my question is this: If I leave my current dojo to go practice with someone else (maybe one of the runaway sempai) am I committing a huge breach of protocol? I feel like I would be insulting sensei to do this, but I also feel like I need to find someplace where I get positive energy when I'm on the mat. Any suggestions?
Depends on what you want out of your training, doesn't it? Did you start at this dojo because of the energy and flow of the classes, or because of the sensei having to teach you something you wanted to learn?
No committed teacher is happy to see their students leave -I'm a teacher, I know!- but it's their problem, not yours. You can choose the manner in what you leave, though.
I've watched the energy at my dojo ebb and flow, but I stay, because I believe in the training and in my teachers. YMMV.