I think the most important thing you can do is emotionally separate yourself from your husband. I personally can understand staying together (particularly for kids. I would do it), but I think you need to be realistic and start thinking of yourself as more separate and taking care of you. That way you are prepared either way... because this thing can go either way.
Even if your husband stays in an unhealthy place, and cannot work through his problems, the more you are involved with him, trying to help him, trying to fix things, going through success, failure, success.... that's only going to tire you out, and create resentment on your part (and may even make him feel like you are controlling him, or trying to direct his life). He needs to fix these problems on his own. Also, I think he will need to find his way back to the marriage on his own.
I think you should emotionally protect yourself, be a friend and good listener, but still give him lots of emotional space and distance to take care of his own stuff. Expect him to fail.... that way if he does you wont be crushed, and if he doesn't after 5 years, you can be pleasantly surprised. Create a life for yourself that will be great with or without him.
You're getting lots of good advice here on your thread... you'll have to figure out what snippets of wisdom you want to apply. I Believe you are strong and wise and will figure out the best path.
There is no arriving, ever. It is all a continual becoming.
