Hi OP, this sounds like such a difficult thing to go through for you. Does your Mum have a diagnosis?
Lots of people on here are assuming that your Mum is the way she is because of her relationship. Of course there are shades of grey. That's one of the possibilities and another is that she has a mental health illness that leads her to be depressed sometimes and out of character at others where rational judgement deserts her.
I am taking you at face value from what you have seen of their relationship over the years, in which case your Dad has had a breakdown rather than this being a pattern. If this is the case, no, I don't think you push for any reconciliation, because, if he has broken down again, there could be a next time, and if your Mum continues to have episodes, next time he could kill her and next time he may step in front of that lorry.
Sounds like they both need looking after, that's not something you can take on to your shoulders, you would do best right now perhaps to find support groups for families of those with mental illness so you can share with others who have had to go through the difficulty. You local mental health service, if it is a good one, may organise family support groups, do look into it. The charity MIND might be able to help you in finding support too.
Having a Mum with a chronic mental health condition, if this is the case of why she has had these episodes in her life, is not easy. When you don't suffer from depression or manic episodes etc., it takes a lot of understanding to realise that the person is not doing these hurtful things on purpose, that they are out of control, just as if they were full of the symptoms of the worse flu ever. We know that when Mum has flu, it's not her fault, it is so hard to get our heads around that when it is mental health. Try not to be angry with your Mum although it is important to acknowledge how sad it makes you and how difficult it is. Sounds like you want to protect your Dad because he has been there for you and more steady in your life. You cannot and must not try to control either of them.