Jax will eventually get its act together downtown. This JAX to BUF trip is all of getting inspiration from BUF's DT and nothing else. Let's not act like Buffalo as a whole doesn't have major issues. Most dying/ soon to be dying major metros like Chicago, St Louis, Pittsburgh and Cleveland have enough "meat on it's bones" to still be major cities for the foreseeable future.
If Buffalo keeps on losing people, it will eventually be headed into the sub-million zone in metro population, that's almost like being relegated (soccer analogy). Also, there are alot of metros that's around a million in pop (like Tucson, Grand Rapids, Fresno and Tulsa) that are waiting in the wings to easily push Buffalo even further down the metro population scale. Yes, keep on losing enough people and a downtown can even be affected; it's not unpresented.