I am from california and our FMLA here also only lasts 12 wks. After my FMLA ended I had to send a letter from my doctor to my employer, letting them know I would need to be on leave longer. Unfortunately the law doesn't require my employer to hold/save my position longer than the 12 weeks. Fortunately my employer has been very supportive and they have advised I am welcome to go back to work when I feel better. Of course leave is unpaid but as soon as you stop working you need to apply for disability to have some sort of income.
This is a good question to ask the rest of the community so please use the "questions" section. You will get more responses from people that way. I read your post by sheer luck since I was looking at profiles of new people diagnosed with cervical cancer. Please let me know if there is anything else I can help with. Sending hugs your way.