If dad is a drinker, is it better to keep him till kids graduate or divorce now?

Seek support. I would encourage you to seek support, find a good counselor, try an al-anon meeting, this is a place for loved ones to go if they are affected by someone else's drinking. This is not a question I can answer for you, with proper support you will be able to figure out what you need to do. Seek help so you can find your "healthy voice". This may help steer your husband in the right direction as well.