Maybe I misunderstood, but if the writer doesn't want it to be for commercial purposes, then you shouldn't try to make money from it? Or, where do you think the income will come from?
In general though, the income split is in favor of the artist, as drawing takes longer than writing. I don't remember the exact percentage off the top of my head, but I'm sure someone else does!
But really, I recommend that you communicate with the writer on this question. If you want to unlock income possibilities, but the writer wants your project to stay non-commercial, you have to come to an agreement beforehand, or you risk running into conflict later on, which would suck for both of you.