I doubt citrus, as a genus, will go extinct. There are too many species and varieties with different characteristics and adaptations that will enable at least some citrus to survive. That being said, as much as I love citrus, they do seem to be quite susceptible to disease pressures. Thankfully, since mine are hundreds of miles away from where they are supposed to live, they are also hundreds of miles away from the pests and diseases that want to kill them. They only have to worry about my ineptitude killing them.