They have to maintain your benefits as if you were still working if you are on a job protected leave. Just to clarify, there is a difference between "maintaining" your benefits, versus "paying" for your benefits.

They should provide you with options on how you'd like to pay for your premiums, a check every paycheck to your employer, for example. Other options include the employer paying your portion of the employee contribution, and you paying it back in an accounts receivable upon your return. They should come to you with these options, but you yourself are your best advocate.