Mike beat me to it
I would add though - what is your gut telling you? Sounds like it's telling you to run and don't look back.
It's been my experience that my gut often chooses a better path than my head does. I'd listen to that gut.
Also, they have a long history, you say your dad is still drinking, and you don't know what the deal is with your mom. Unless he gets sober, and she gets counselling, I'm guessing absolutely nothing will be different. Will they be hurt? yes. Is that your problem? no. Not unless you get back into their lives, wait for the honeymoon period to wear off and then they'll use your 5 month period of detachment as yet more ammunition in their pool of toxicity.
Nothing changes if nothing changes, and it sounds to me like nothing's changed except for your absence.