I don't reckon father's are indispensible, just as I think a child can be perfectly happy without a mother. (Well; apart from the trauma that society imagines the child to have over this, which eventually becomes real to the child...)

I think a rolemodel of each gender is preferable to have, but I've seen plenty of examples of these being provided by soembody who happens to have had nothing whatsoever to do with the actual conception of the child...