My brother is like this and has cut off all contact with our family. He's heavily codependent and in a mutually abusive (physically and emotionally) marriage.
If you were my friend (from before) or my relative, I'd want you to reach out to me. I can be there for you after you leave. I am not strong enough, however, to stand by and watch the abuse.
If you have any friends like this, please reach out. I periodically reach out to my brother, but only a couple of times a year. So I have no clue if/when he will ever need moral support to leave.
As an alternative, when I have left relationships, I feel absolutely despondent. Even if I do the leaving. In these situations, I immediately created new routines for myself. I like to read and I like to go to movies by myself. So I'd hang out at Barnes and Noble with coffee and a good book. Or I'd go to movies. I took up kickboxing once. Imagined kicking the dude in the face over and over and over.

Took a cooking class once. Started up a Sunday night dinner rotation with my friends. Each friend would cook dinner one week. Everyone else brought their favorite wine or beer to try. Book clubs. I just saw a pottery class advertised at the local community center. Join a gym or up your attendance.
And as a mom, I find my kid is a HUGE time suck. So that's a great mental diversion for me, from sadness and fear. I focus on my kid.
You can do this. The first few weeks will suck. Know that. Know that it will get better. And create new routines. After awhile, you will find them comforting. And then you will start looking forward to them.