My father was unpredictably violent, self-absorbed, and extremely controlling (removing all light bulbs from sockets, turning water and heat off to 'punish' the whole household as an example).
My mother withdrew into a deep depression in her bedroom and hardly ever came out, leaving us children to raise ourselves and duck and dodge our father's insane tempers.
Neither of them worked, all of us children were homeschooled, so the house was a 24/7 pressure cooker.
I used to beg my mother to leave him, as everyone in the house was utterly miserable, and she used to say she was waiting for the youngest kids to grow up. I feel guilty for it, but I hated her so much for that, almost more than I hated him (and I'm another who used to fantasize about stabbing him, just to save us all).
After approximately 20 years of that misery (and after I'd left home), she did leave him.
The children who were raised within the marriage (including myself) = breakdowns, hospitalisations, self-harm, suicide attempts, substance abuse, terrible relationships.
The children who were mainly raised after the split-up = happy, confident, sociable, generally thriving, affectionate relationships
The difference between the two groups of siblings is extreme, and based on my experience at least, I would never stay in an unhealthy relationship "for the children's sakes". It was so soul-destroying, and not only do I still harbour a lot of hidden rage against my mother for not protecting us, I have a hell of a lot of self-hatred for being the 'reason' she stayed.