There's bad news and good news. Let's get the bad out of the way, first: there will be a time when Herrmann decides to call it a day on Chicago Fire. The actor who plays him, David Eigenberg, talked about the character getting older in season 12, and how the firehouse around him is changing.
He not only acknowledged the changing of the guard at the 51, but Eigenberg told The Hollywood Reporter that he knows he will eventually have to make way for firefighter characters who are fresh and can keep the show thriving (depending on how long it stays on the air, of course):
"[There's a] changing of the guard. There'll be a point where it’s like, yeah, I guess I gotta pass the torch."
It's a sad reality to confront, but it makes sense. Christopher Herrmann is in his early 60s, and the mandatory retirement age for Chicago firefighters is 65, so he's legally unable to his job for much longer.
David Eigenberg knows his character is aging
There's also the fact that Herrmann recently suffered an injury that required him to start wearing hearing aids. The character was reluctant to get the ringing in his ears checked out, but his ability to get past his pride and embrace his hearing aids suggests an acceptance of getting older.
Eigenberg talked about the difficulty of performing Chicago Fire stunts as he gets older, and how he has had to come to grips with the fact that his tenure is winding down:
" It’s real for me in this show, because it’s so physically demanding that there will be a time — [but] I hope the show goes on for a long, long time."
Let's pivot to the good news.
Eigenberg is hopeful he will stick around
Eigenberg doesn't think he will have to pass the torch right away. The actor doesn't intend to leave the show for a couple more years, especially since he's now able to wear his hearing aids on the show (he requested that writers incorporate the devices into the story since he has to wear them more often now).
The actor also assured fans that Herrmann will tough it out, despite having a relatively rough start to season 12. He'll regain his footing, and get his rhythm back as the rest of the season unfolds:
"I have a feeling Herrmann is going to be OK. So, we will see."