My opinion on the "missing parent" issue is children will only look for a missing parent if there is a parent missing. If a single mom or dad is enough of a parent to account for a mom and dad (and most, in my experience, are) then the child won't feel there is a void and won't feel a need to fill it. If the single parent isn't enough and there isn't a grandparent/aunt/uncle/family friend whatever, to pick up the slack, then they child will go looking for what is missing.

My experience--My folks divorced when I was very young. My Mom is one hell of a Mom and we never wanted for anything important. I hadn't seen or heard from him in years. Since my daughter's birth, my father has wanted to get involved in our lives again and honestly, I don't want him there. I don't feel a void in my life of having him not play a role in it so now he is extraneous to my life. In fact, the worst times in my life are when my Mom thought she should provide us with a Dad, not with someone who made her happy.