Amarei, your speculation is as far fetched as you believe other posts to be.
You've not been the product of toxic parents? If not, you have literally no clue as to what some parents are capable of.
Without the ranty letter, there would be benefit of the doubt
Without the walking out in a child, leaving her to an at best unsatisfactory man, at worst she knew he was abusive... There would be room for manoeuvre, a little grey area.
Some things can't be forgotten, bells can't be unrung.
Very very few people go nc with their parents for no reason.
It may be they have their heads turned by toxic others, naturally, but otherwise no. Not IME, it's such a horrific thing to contemplate and live with, it's never done on a whim.