Don't know if my coworker will see this but fmla is very strict about how long your job is protected for. If you wished for an extension you should of done it a couple months before the expiration date expired. Not after it did. Now you're just screwed. Please consider worker retraining programs through the state. The state can offer good training programs for career changes. Due to the fact you're probably disabled from ever lifting more than 25 lbs I suggest light duty careers which do exist. Do not think you're career is over. When one door closes another always opens. 

Now that you're gone my company can finally replace you. I feel bad for you but you can collect unemployment until you figure out that next path. We've been short staffed for most of the year and this just added to the stress.