Being on FMLA only protects you from terminations regarding FMLA-related absences. It does not protect you from terminations that are unconnected with your absences or that would have happened regardless of your leave. If the plant is closing, you have no more right to employment than anyone else. You get your notice exactly the same time as everyone else and you get laid off at the same time as everyone else. The FMLA is immaterial.