I'm sorry that you are struggling so with your mom's addiction and your dad's enabling , but you have come to a great place for support.
It's been my experience that ultimatums aren't very effective if the motivation is to change someone else's behavior. In other words, losing you, sadly isn't a magic means to have mom and dad get help. I wish it was. You'll probably read quite a bit here about "boundaries," and the concept is to establish boundaries for what is both safe and healthy for you, rather than change someone else.
I think it was great that your recognized that being on the roller coaster wasn't healthy for you. Maybe for now, as you work on taking care of your own needs, making a final choice on whether to maintain contact is something that can wait for a bit? If you make a choice to cut ties forever in hopes of changing your parents, I'm afraid you will be hurt and disappointed. If we could love our addicted loved ones into recovery - or threaten them into it, or find the best possible ultimatum, I don't think there would be a need for this forum.
Two things that helped me tremendously as I dealt with the effects of having addiction in my life were to think about my motives, and if they were ultimately about trying to change someone but myself, to step back and wait; and to realize that the impact of addiction on my life, and my own traits that needed some work didn't happen overnight, so I should try to take little steps to work on me and try not be too impatient with myself.
It sounds like you are taking great steps to help yourself. Perhaps considering adding some counseling to help with addressing the abandonment and sadness may be something to consider as well? I hope you'll continue to read and post here - there are many folks like you who understand what you are going through. There is also a forum here for adult children of alcoholics and addicts you may wish to explore.