The reason a lot of viewers became invested in “Chicago Fire” in the first place was due to the dynamic between Kelly Severide and Matthew Casey (Jesse Spencer). The two put out dozens of literal and metaphorical fires, all while trying to find happiness in their personal lives. However, a massive blow to the series was hit when Spencer decided to leave the series in Season 10. His character was written off the show by going off to Oregon despite still being in a relationship with Sylvie Brett (Kara Killmer). The two tried to make it work long-distance in the beginning before finally breaking it off.
The point is Casey’s still out there, and with Severide leaving a massive hole in the show in his wake, now would be the perfect opportunity to bring him back. There are a couple of other characters who are still on the show who have been there from the start, like Mouch (Christian Stolte) and Joe Cruz (Joe Minoso), but Severide and Casey were consistently the heart of the show. They had the biggest plot points, and audiences connected with their characters the most. With both of them gone, it just won’t feel like the same show.
It’s unclear if Taylor Kinney’s absence will be temporary or permanent, but in the meantime, it would delight fans to see Casey back at the firehouse. It would make the show still feel like “Chicago Fire” and could even bring some fans back into the fold who may have stopped watching after Casey left. He’s come back before, notably in the Season 10 finale when Severide married Kidd, so it’s obvious Spencer is still welcome back. It’s just a matter of having him return in a longer capacity.