TV can be a predictable beast with many shows operating out of the same bag of tricks. So in most cases, it's safe to say when a long-absent character returns unexpectedly, it's because they've been marked for death. Here are some prime examples of TV characters brought back to shows just in time to die.
Lundy was brought in during Season 2 to help with the Bay Harbor Butcher case, and eventually became Deb's love interest (despite the huge gap between their ages). He left at the end of the season and wasn't around at all during Season 3. During Season 4's Trinity Killer case, though, Lundy returned to Miami. Just after restarting his romance with Deb, he was gunned down, fueling Deb's need for revenge.
Max Fenig, "The X-Files"
In the show's very first season, Max was a likeable guy who ended up being abducted by the end of his episode. He came back in the fourth season...as a corpse. That two-parter explained how his dead body ended up in the airplane wreckage (and what the implications would be).
There's also the Cigarette Smoking Man, who viewers thought was dead after the seventh season. Surprise! He comes back in the series finale, only to be blown up by a missile of all things.
David Palmer, "24"
After being at the center of the show for three seasons, David Palmer didn't really do much in Season 4. When he appeared in the premiere episode of Season 5, he only stayed alive for about a minute before being assassinated. Dennis Haysbert, who played Palmer, was not happy about the decision.
As he told one reporter when asked about whether he argued with producers about the exit for his character, "We didn't really have an argument about it; I just refused to do it for a great many months...They said they really couldn't do it without me. I acquiesced, but if I had to do it over again, I wouldn't do it."
The Cortexiphan Kids, "Fringe"
In the two-part Season 2 finale, a whole host of former Cortexiphan test subjects are brought back to help Olivia cross over to the alternate universe. Nick Lane, Sally Clark, and James Heath all die during the resulting altercations. It's too bad; they made a great addition to the team.