My granddaughter is 3 and sees her father on an irregular basis. Do you think this is more stressful...?

My daughter married a man who abandoned them 2 years ago. He is an alcoholic and very undependable. My daughter has 100% custody (physical and legal) and is a wonderful mother. She has allowed her ex to see his daughter, only when he is sober and she is there to supervise, but when he's on a binge, he makes plans with his daughter then forgets them. She loves her daddy and he loves her. Do you think it would be less stressful to never see her father or continue to be disappointed? I'm not saying what my opinion is so please, don't be rude.