Be honest, but like you said...no character assassination. I do think your boys are slowly figuring things out for themselves, but it will be good to sit down have a talk and see what questions, if any, that they might have.
I know you'll do this, but reassure them that it is not their fault that he walked out and that they are safe to talk to you about anything w/o fear of being punished.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
