If your FMLA has expired, your employer is not required to hold your job any longer. There is no requirement that you receive severance regardless of whether they use the word "terminated" or not (unless provided by legally binding policy, contract or CBA). Severance is never required by law in 47 out of 50 states and is not required in these circumstances in the remaining three. It would be rare indeed for severance to be offered to someone who is unable to return to work due to medical reasons.