Dirk Benedict is alive and still working... Rose has a vague memory that they tried to get him onto the show but he declined, reason not known (may have been a scheduling conflict).
Looking on IMDB, he did lend his voice to a BG video game put out in 2003. The game setting was 40 years before that of the show, though... looking at his character name, he may have played the father of the current Starbuck.
Yeah, I checked IMDB, too, for Dirk Benedict. Looks like he's still working. Maybe there just wasn't anything he wanted to do on the new show.