The general rules are:

If and when you are denied legally protected leave, or are illegally discriminated or retaliated against because of requesting or taking the leave, or you are refused accommodation, then you can consider legal claims.

If your CA employer has at least 5 employees, they can not fire you because you are pregnant, must allow you to continue working as long as you are able, must 'reasonably' accommodate your disability, and must allow up to 4 months of unpaid pregnancy leave under FEHA.

If your CA employer has at least 50 employees, and you are employed for at least 12 months, have at least 1,250 hours worked in the 12 months prior to the leave, then you would be eligible for 12 weeks of unpaid FMLA / CFRA maternity / medical leave when you are unable to work [or must care for an immediate family member] because of a ‘serious health condition’ that is properly confirmed and documented by your doctor, continuation of group health benefits, restoration to the same or an equivalent job upon return to work, with accrued benefits. The leave may be taken on reasonable intermittent basis if that need is properly documented by your medical provider.

If you qualify for both, you get both. If you are out longer than those guarantees, they can fire you.

Overriding those stated protections, just because you are on leave does not mean you can’t be terminated. You have no special exemption against lay offs due to business reasons. A company in downsizing can lay off a FMLA leave person, as long as they can show they aren’t targeting ‘because of the leave’. They are simply risking claims if they do.

If your company has a policy requiring they hold your job for you for a specific period of time while on disability, that is enforceable.

Upon termination from employment, you are entitled to COBRA conversion of your medical benefits [if any], allowing you to pay for and retain your insurance coverage.

Now, if they violated those rules, contact me for the legal help you'll need. I'll be happy to do so. I've been doing these cases for over 20 years.