caution!
remember, for an I-485 AOS case, YOU are the client, and the lawyer is representing you, regardless if s/he is being paid by your employer or not.
as such, when you have filed a G-28, you have - in essence - given a power of attorney to the lawyer to take actions on your behalf. conceivably, if the lawyer wrote to the BCIS that s/he wants to withdraw the case, it could be assumed that s/he is acting under your instruction or consent.
however, if a lawyer does that without your consent, then they could be in serious breach of the applicable laws and guilty of professionaly misconduct. at the most a lawyer could withdraw HIMSELF from your case, but cannot withdraw your case without your instruction.
if you are fearing any drastic action from your lawyer, i suggest you consult another attorney immediately, and seek their counsel.
please keep in mind that the above is not a legal opinion or recommendation, just a personal opinion. please do consult a qualified immigration lawyer before any decision.
people have been screwed over by their lawyers through incompetence, or worse... don't delay, seek help from another lawyer.