Dean was kidnapped by his mother Sharona at the end of Deathlands #66 - Separation, released all the way back in June of 2004. By the time he appears in Prodigal's Return he will have been gone from the series for over seven years in terms of publishing history, and for over three years in terms of story continuity. My understanding is that he will not join the group again at the end of #100, but will return on a permanent basis several books later. Of course, I could be completely misinformed on that point.