I would start by contacting your union and if they don't represent you get your own legal counsel. You can find a good employment lawyer willing to be paid on contingency which is usually about 1/3 of what you recover. First, you need to find out what they mean when they say they "replaced you." Did they hire another teacher to take over your class but will continue paying you so long as you are able to make it in the building? If so, that may be legal. If not, and they simply are firing you for using FMLA, that is illegal. Employers are required to make REASONABLE accomodations for people with disabilities. While intermittent time off is often an accomodation, in the teaching field it is less likely to be seen as "reasonable" if it is for long period of times. Try to get a copy of your job description and contract for your attorney. If it says something like "providing a consistent learning environment for children" then they could argue you can not do an essential function of your job. You are not protected under the ADA if you can't meet the minimum qualification/essential functions with or without reasonable accomodation.
Next, unfortunatly, they are only required by law to protect your job and benefits for the 12 weeks. If you use more than the 12 weeks they can drop your benefits unless your contract says otherwise. You are still elgible for COBRA (which I know is little consolation).
Contracts vary regarding what benefits you maintain on disability. However, your employer does NOT have to protect your job beyond the 12 weeks even if you go on short or long term disability, unless your contract says otherwise or your local state law says otherwise. So your disability policy might buy you some time to get better and find a new job but it most likely won't protect your job.
I understand that you have a contract but you not working could be considered "breach of contract." However, breaches in service contracts due to personal illness excuse performance. So, in other words, they couldn't sue you for not teaching but, since you are not teaching, they might not have to hold up their end of the bargain. Performance could be excused all around.
Now, none of this is legal advice, just stuff I have picked up over time. Most contingency attorneys will offer a free consultation. You should take advantage of that and see what they think your options are. Check back and let us know how you are doing.
27 Year old married female. Graduated law school this year and waiting for results of the bar exam. Start a new job sometime in September. Diagnosed w/ CD 4 years ago, IBS for over 10 years before that, which was probably the CD. I am sort of lactose intollerant too but can handle anything cultured and do well w/ lactose pills and lactaid. For crohns I am currently on Pentasa 4 pills/4x day and hysociamine prn. I also have bad acid reflux and have been on PPI's since age 13. I have been through prilosec, prevacid, and nexium. Currently I am on Protonix in the morning and Zantac at night. I take xanax prn for situational anxiety (aka no easy bathroom access).