WIBTA if I gave my sister an ultimatum over taking her husband back?

My (34F) sister (32F) married a really awful guy (35M) about 12 years ago. Let's call him Frank and her Lisa. I knew Frank in high-school and he was an awful person then. Think of the typical douchcanoe that gets by on his looks and smile but doesn't have a real personality underneath it all. We had similar friends but he went AWOL during senior year. Turns out he dropped out, got his GED and left the state. Years later right while I was planning my own wedding, this guy pops up on my FB and I find out through my mother he has been sniffing around my sister after meeting her in a bar back in out hometown while he had been visiting. I let them both know then and there he wasn't worth a dime and to leave that dog where it lay cause he was trouble. I got told to shut up (FYI this isn't the first time ppl have told me to shut up about someone and now both times I've been right. The other instance my cousin married a man I got bad feelings about and it turned out he was physically abuing her) All this time he's a massive alcoholic and she knew it, but didn't tell us. Fast forward a few years, she marries him after he convinces her to stay a school she didn't want to for post grad cause he didn't want to move. (She had no scholarship offers at this school, but full rides at other universities). Within 6 months of the marriage he up and moves away to a whole other state for work but she's stuck where she is cause she can't switch programs once she's started. So she spent 2.5 years alone with him getting to play bachelor in another state. I had warned her this was a red flag. She eventually graduates and moves to him, she spends 6 months studying for her final certifying exams and she ends up playing maid everyday to fix the disgusting apartment she walked into that he had been living in. He promised he would take care of a house better cause it would be his (you see where this is going). More years go by, and his rampant alcoholism becomes a problem to his health and his burgeoning hypochondria. They buy a house and (you guessed it) he does nothing. Never cleans, never fixes, never helps out, nothing. My sister works 60+ hour weeks and he sits and drinks. He has a job that a buddy got him but he constantly lays out due to health issues the drinking causes. I kept begging her to leave him, she doesn't. Then she works for 13 months to get pregnant. Needless to say things only get worse because of course it turns out this man passed on health conditions to thier child and he just drinks even more, claiming its cause he's so worried for the child. I begged her to leave again. Nope, she just gets a better paying job and then they go and have a 2nd. During thier first child's second round of health issues, right after the 2nd is born, she calls my crying. He had left the hospital to get drunk while she sat there with a screaming scared 2.5 year old abd a 6 week old trying to hold it down. She makes the decision to move closer to us. Here they come, all 4 of them including crappy dude. Fine, whatever. It only takes him 3 months and he has a full alcohol induced meltdown and shoots up thier house after mixing alcohol with dr*gs. Luckily my sister had left with the kids to my mom's house cause he was acting strange. Now he's in a rehab facility ordered by the state, she's started paperwork for seperate maintenance (think legal separation not divorce), he's got no job and they're going to loose everything. If this isn't enough for her, he's playing at rehab, moved into a facility that let's you have day passes, going to concerts and basically living it up on the states dime. And his own, he's drained his account. My sister took her half of the money out but she can still see his. Now he's on social media pining after her and wanting her back and she faltering. I know I can't stop her from going back to him, but I'm done. I've been second parent for almost 6 months now, even before he lost his mind and blew bullet holes through every room in thier new house. I kept her child at my house, drove him to appointments and continue to do so. WIBTA if she takes him back and I shut her out of my life? I can't have him around me, my kids or watch her suffer cause thats all shes going to do. Should I tell her now how I'm feeling, or should I wait and see what she does when he is released in a few weeks. She put herself in therapy and her own therapist is struggling to get her to see how going back is delulu.