But Vorik was just an ensign. He was never shown to be high-up in engineering. In fact, it was explicitly noted that lieutenant Joe Carey was B'Elanna's immediate subordinate.
And I recall reading an interview with the actor who played Carey that he would have wanted more appearances. I don't think it was because he was too busy. It was odd they brought him back years later just to kill him. I guess they thought it would add emotional weight. But after such a long absence, most people probably didn't know he wasn't a one-time extra.
And yes, Chell did make a couple reappearances, but he looked like a completely different person. They really drastically changed his Bolian makeup.