If you can prove that there was something wrong with their machine that broke off your mirror you do have legal recourse. Try talking to them and working it out. If they are unreasonable, you can bring an action in small claims court without having to pay a lawyer. There are no lawyers in small claims court so they can't have one either.
In my experience, that California DMV rarely enforces the rule requiring filing an SR-1 form. They have the right to, but I don't see them doing it very often. A more practical question is whether you had autobile insurance at the time of the accident. That is a rule that they do enforce, assuming they know about the accident. Good Luck
I would need more facts to answer the question properly, but I would guess that the lawyers amended the complaint for the benefit of the case. I suggest you sit down with the lawyer in an effort to better understand the strategy
It is possible the case can be settled through ADR but you cannot force it to ADR if both sides don't agree. Once you go to small claims court, your insurance company will pay any judgment against you. Good Luck