Word of God has given two answers to this. When the show first came out they said that he was dead; however the later started saying that Rebecca was divorced. I find it odd that they waffled on it. Either they didn't think about it in detail or they didn't like saying she was divorced. I'm pretty sure divorce was still very frowned upon in America in the late 80s early 90s so they may have said he was dead to avoid the discussion.

Cute! I'd say her Daddy is either dead, estranged or in jail.

Beautiful :D