FMLA offers 12 weeks per year, not indefinately, or per medical issue. Sounds like your 12 weeks are up on Sept 15th. After that time, they do not have to hold a position for you.

If they let you go, you can continue your insurance through COBRA, or look into seeing if you qualify for Medicaid or some state sponsored low cost health insurance that will set your premiums according to your current income.

Was this a work related foot injury?

You can get a medical "recertification" from your doctor because you've had multiple problems (cancer, then the foot surgery). This would entitle you to an extension of your FMLA time.

There are stiff penalties for employers who dare to retaliate against people in need of FMLA. You would have a major lawsuit against your employer if they give you a hard time.

Make sure you contact the federal agency in your community and set things up exactly the way they should be done. Get the doctor's certification in writing, photocopy it, and send it to the top brass at your company.

Lawsuits have been so heavy that companies have been put out of business paying big judgment awards to people on FMLA, for interfering with their rights. It's a federal offense.