After maternity leave, can an employer have you pay back both your health benefits payments as well as their health benefit payments for the 12 weeks off?
If you returned to work, they cannot require you to pay or repay that portion of your health insurance which they normally pay for. They can require you to pay your normal portion of the cost of health insurance, if you did not pay it and they picked it up at the time. They have to maintain your health insurance, but don't have to pay more for it than they normally would.
If you did not return from maternity leave or returned for only a de minimis time (e.g a week) before quitting/resigning, they can require you to repay them their portion of the health insurance premiums they paid while you were on leave. Maternity leave is founded on the idea that it is a temporary leave from work and you are returning. If you don't return, it is considered that you did NOT in fact take maternity leave, but simply defrauded your employer into paying for benefits when you had left employment and were not otherwise entitled to them.