I am a father with "abandonment issues" with my own father and was an elder for more than 20 years until I walked away three years ago. There's been a lot of very good advice posted here already, some of it conflicting. My two cents:
You're are letting "the book" get in the way of your judgment. In doing this, you are like the person who says "as soon as i win the Lottery I am going to change my life." Your odds of writing that book, much less getting it published, are incredibly remote. I'm not saying you can't or won't, but to put a relationship with your father (which you appear to want very much) on hold because you might write a book (or win the lottery, for which the odds are about the same) is a mistake.
Deal with your father first. Live the life that's right in front of you. Who knows, it may make you a better writer and help you produce an even better book.
Your father is like many elders I have known (including myself). He appears to be a company man, "all in," but in fact he is thinking for himself. The abuse issues within the family have no doubt made him do some serious soul searching and thinking. The fact that he made that call to you and opened up the lines of communication - without, as far as I can tell from your post, imposing any conditions on you - says a lot. I think you should take him up on his offer to build a relationship, but do it on your own terms. If he's just posturing, that will be clear soon enough. If he's not, you may be surprised at the breakthrough possibilities.
When I could no longer "do" this dub thing, I was afraid to tell my wife how I felt; but since she is my best friend, I confided in her. To my surprise, she was on the same page and we exited together. We both had some concerns about our grown children, three of whom were fully ensconced in the witness world. But we leveled with them, telling them that we loved them unconditionally and that it did not make any difference to us what religion they embraced. Then we held our breath, hoping they would accord us the same slack. The results were simply amazing. Today, all three are out, moving on with their lives, and much happier for the freedom they possess. We "saved" our family by showing the courage to open up about our doubts and concerns and walk away from a toxic religious environment.
I believe this was divine intervention from above. The universe, or God, or whatever you believe your higher power to be, rewards honesty and courage.