It seems to me that you did a brilliant job in a tough situation. You acknowledged and validated their feelings while not lying to them or being dishonest or negative about their father's behaviour.
I'm impressed that you gave them the message that they are not responsible for causing or fixing their father's behaviour. I think you gave them a strong life lesson there.
Much as they miss their father, I honestly think that with a parent as strong as you, they'll do very well in life.