NCISis one of the longest-running procedural dramas on television, and for good reason. The stories are captivating, themes relatable, and characters believable. Over the years, the cast line-up has had multiple changes, though not necessarily for the better, and fans have been crossing fingers and praying to see a few return in season 20.
For some characters, departures are permanent, having either been killed off on-screen or their actors have passed on. However, there are a few that simply walked away from the job, leaving them a perfect window to return -- even if it's just a quick visit.