We're still processing the news that Darren Ritter will be leaving Chicago Fire. NBC confirmed that the veteran character will be written off the series before a hypothetical season 14, despite being a part of the team since 2018.
It's difficult to imagine Chicago Fire without Ritter's presence, and it's evident that this news has had an impact on the actor who plays him, Daniel Kyri. He took to Instagram shortly after confirmation of his exit was made public, and made it clear that he was heartbroken.
Daniel Kyri praised Chicago Fire fans

"I’ll miss this character, and it’s time to move on," Kyri wrote on his Instagram Stories. The actor also made a point of thanking and praising those responsible for his beloved tenure on Chicago Fire, fans included. "Thank you to the cast, crew, & the awesome fans," he added.
Kyri's character was confirmed to be leaving the show at the same exact time as Jake Lockett's Sam Carver. Both men have been cut from the future of Chicago Fire due to NBC's desire to keep costs for the episodes low. Deadline noted that the series has already taken steps to remove characters from episodes in which they are not absolutely needed, but this marks the first time they've been taken out completely.
Interestingly enough, Ritter has only missed one episode of season 13 so far, "Born of Fire." While more prominent characters like Stella Kidd (Miranda Rae Mayo) or even Carver have been MIA for a couple of storylines, Ritter has been present for most of the season, which makes his impending departure all the more surprising.
Kyri's Chicago Fire exit details remain unclear

It's unclear whether Ritter will be written off the show in the lead up to the season 13 finale, or if he'll appear in the rest of the episodes and "exit" in the space between seasons 13 and 14. We've seen it happen before, where a character explains where another character went with a line of exposition. It can actually be easier, if a show doesn't want to go the dramatic route and kill a character off or lean on a tragic reason for their departure.
We saw this sort of understated approach take place with Ritter's old friend, Blake Gallo (Alberto Rosende). The character quickly decided that he was going to move to Michigan, and had a brief, albeit emotional goodbye in the midst of an episode that otherwise had nothing to do with him. We hope Chicago Fire does Ritter justice, given how beloved he's become by the fans.