Besides, Squad firefighters are hard to find, and the newcomer to Firehouse 51 can’t just step into Severide’s shoes if Severide does depart.
After all, Gabby Dawson is shockingly returning in that episode; could she talk Casey into returning to Puerto Rico with her?
At the time, Derek Haas only confirmed that either Casey or Severide would be gone from Firehouse 51 by the end of the midseason finale, and it’s still possible that Casey could make an exit rather than Severide.