Actually Chris, I doubt if that sort of change will have much impact on koryu. I'm not saying they won't continue to evolve and grow, they will. They are living arts rather than fossils.
First though, the koryu don't change to adapt to students. Students change to adapt to the koryu, or they leave. So there is no push here for them.
People leave - that's how things change, that's how it's always been - even in Aikido. I agree though, that with the limited number in most koryu means that change is usually quite slow.