Warning: spoilers ahead for Episode 11 of Chicago Fire Season 9 on NBC, called "A Couple Hundred Degrees."
The second half of Chicago Fire Season 9 has taken two surprising turns when it comes to Brett and Casey: seemingly pressing pause on a Brettsey romance despite a lot of setup and revisiting Casey's head trauma. Casey got a lot more than just a bump on the noggin to leave his future at CFD in jeopardy, while Brett moved on to a relationship with a cute firefighter from another firehouse. Their storylines seemed to be diverging, but Brett's decision about Casey in "A Couple Hundred Degrees" could impact the rest of Season 9.
Despite some reservations about spending a full night with him, Brett agreed to go on a quick ski trip with Grainger and seemed to be looking forward to it, but quickly decided to cancel when she learned that Casey was planning on making an appointment to see a doctor about his head on the same day as the trip. She offered to go with him, and Casey accepted. So, does this mean Chicago Fire is going back to exploring a Brettsey romance, or Chicago Fire going back to the friendship that helped Brett through some very tough times in Season 8?
For me, a lot depends on the endgame for the plot with Casey's head injury. If Chicago Fire is simply delivering a juicy story for Jesse Spencer in Season 9 that will be resolved in time for him to return as Casey in Season 10 and beyond, then I can see this as Fire at the very least making sure to keep the Brettsey door open for the future. If this juicy story is leading to Casey leaving CFD, however, the return to Brettsey might simply be the two characters moving past their post-kiss awkwardness and rebuilding a platonic foundation as friends.
It's too soon to say one way or the other with any certainty if Chicago Fire is setting up a farewell for Casey, but for Brett's sake, I certainly won't wish for Fire to fan any relationship flames only for her to have to say goodbye to Casey if he is on the way out! The poor woman has already lost partner after partner over her years on Chicago Fire, and she and Casey were always great as friends.
Besides, her decision to cancel on Grainger to go with Casey to his doctor's appointment hardly qualifies as a grand romantic gesture on its own. Casey needs support, not least because bringing somebody along guarantees that he actually goes through with visiting a doctor about his head. Brett's decision to go with Casey over Grainger proves at the very least that she's a good friend who can prioritize the health of one person over a ski trip.
Whether this leads to Fire revisiting Brettsey after seemingly shifting focus to Brett/Grainger and even Dawson/Casey from afar remains to be seen; whatever happens, Brett's decision to go with Casey (and presumably make sure that he follows the doctor's instructions) could determine the direction of his story after the events of "A Couple Hundred Degrees."