Sounds like the old "follow the money" meme. There are only two examples that I've really noticed. Several book have been published with Robert B. Parker's characters Jesse Stone and Spenser. The stand-ins may be good authors but I had never heard of them. So, I have passed on them. And, then I've seen several books about Robert Ludlum's character Jason Bourne that were published. The stand-in is Eric Van Lustbader. He's a good author. However, after having read two or three of his books, I decided he was not my cup of tea and so have passed on his Bourne books. I guess the reason I don't much care for this practice is that I don't think it can ever be the same as the original author. When it comes to an author's "voice", I think you can imitate but seldom, if ever, duplicate. I suspect that your dad's fans much prefer your treatment of your dad's estate.

Justintime