One doesn't need to be divorced or even separated for that matter in order to stop the derrivative petition. OP's husband is the primary beneficiary and he has all the right to decide whether his wife should be derrivative beneficiary from his petition or not...He can make her petition to stop from processing at any stage of the processing but before his case is decided. Once the case is decided then revocation is very hard, unless there is a marriage fraud issue. He doesn't need to have divorce in order to kill his wife's eligibility for the benefit.
Yes, OP's I-485 and EAD are hers, and not her husband's, and he cannot request to withdraw her I-485 but he can certainly ask the agency to withdraw her from his petition as a derrivative beneficiary. Afterall, he is the primary beneficary for the benefit and her I-485 is based upon derrivates eligibilty from her husband's petition. Further, divorce itself doesn't revoke anything, it's notifying the USCIS about the divorce does.
But again, her husband doesn't need to have divorce decree or anything to make a request to take her name out from derrivates beneficary. He can do that...at any time...and without any reason... and without her knowledge...but of course, he cannot do anything about her pending I-485, but it will be cancelled/denied once he would make a request to USCIS to dump her as a derrivate beneficiary on his petition. Then USCIS will notify OP by a certified letter that her I-485 is denied because there is no eligibility she has anymore for it as her husband requested to remove her name from his petition.