Aside from their participation in 1991's poorly conceived alternate-universe Dallas series finale, in which Satan showed J.R. what life would look like without him (the answer: crap!), Shackelford and Van Ark have not returned to Southfork to see their daughter Lucy since the '80s. In other words: they are major deadbeat parents with some serious explaining to do! In actuality, they have a good excuse, as both were spun off into their own successful primetime soap, Knots Landing, which ran from 1979-1993.
Van Ark made her final Dallas appearance as loopy Valene back in 1981, while Shackelford's reformed drunk Gary last visited his mama Miss Ellie in 1985 for the burial of his brother, Bobby.
Dallas, which returns to TNT for Season 2 in late January, had attempted to bring back the Knots pair last season for cameo appearances, but Shackelford, who also recurs on CBS's The Young and the Restless, wisely held out for a meatier storyline. He got his wish, as I hear he and Van Ark will be on for a three-episode arc. No word if their all-grown-up twins, Bobby and Betsy, will be joining them.
Now, how do we get Donna Mills' scheming Abby Ewing back in bed with J.R.?