I've been thinking about this for a while, mostly since spring 2009 when I changed my major from music education to performance. (Well, technically, to a bachelor of arts.) I asked myself, 'what exactly can I ever do with this degree to live comfortably?' My conclusion was to teach at a collegiate level. Essentially, the main sustainable position toward which I can strive is teaching other kids like me, who have no idea what they want to do, but only know that they want to study music.
More recently, I've been look at this both ways- optimistically and pessimistically. The pessimist in me says, so then what's the point? How can we find a way to make music education relevant outside of our own field?
But the optimist in me says, hey, we can make our own field as relevant as we want. In fact, as musicians, it is our job to promote music every chance we get, as teachers, performers, and audience members. My undergrad's music department has a slogan which describes our music majors as "educators, entrepreneurs, and performers", saying that no student is just one. Educators teach, but also seize music business opportunities and perform at a high level. Performers have a high level of musicianship, but also know how to promote themselves and share their craft. What I've come to learn is music is all about making your own opportunities- collaborating to perform and teach. So is music self-sustaining? Sure...I think we can sustain it.