How sad to see that happen to someone you love. The biggest what-if has got to be: "What if he had stayed with me instead of trying to hookup with the other woman, would he be dying now?"
You're right, if you've said goodbye, then he should see his son in the time he has left. I don't see that a visit would be bad, especially if you could show him he's not alone, but I understand if you don't want to see the other woman.
It's a tragedy for someone to die over alcohol, but only addicts know how hard it is to quit and stay sober.