Warning: The following contains SPOILERS for The Flash season 8, episode 13, "Death Falls."
A major story arc of The Flash season 8 seemingly ended with the death of Frost Snow, the former Killer Frost. There remains some question as to whether or not the ice-empowered anti-hero might enjoy a magnificent resurrection akin to prior The Flash characters, especially given Frost Snow's (Danielle Panabaker) continued popularity. At the moment, however, the rest of Team Flash seem convinced that their frozen friend is truly dead.
Originally introduced in The Flash season 2, the supervillain Killer Frost was an alternate version of Dr. Caitlin Snow from the reality of Earth-2. The Flashpoint incident of The Flash season 3 rewrote reality so that the Caitlin Snow of Earth-1 also acquired freezing powers and a cold-hearted alter ego, but she later came to achieve a state of symbiosis with her other half after discovering her powers with Killer Frost's personality the result of her scientist father's experiments. The Flash season 7 then found Caitlin and Frost separated into two distinct beings with separate bodies after encountering Mirror Monarch's technology. Frost was adopted into Caitlin's family as a sister, but Frost never felt entirely at ease with her new life, fearing that she was nothing more than a clone of Caitlin.
This fear figured prominently in The Flash season 8, episode 13, "Death Falls," when the Black Flame Killer Deathstorm preyed upon Frost's identity crisis to keep her from fighting him. Thankfully, Frost overcame her fears and acquired the power she needed to counter Deathstorm's psychic assault on her teammates. Unfortunately, the stress of her new powers taxed Frost's body beyond the abilities of her healing factor, and she entered into sudden cardiac arrest.
Despite Caitlin's best efforts to save her sister, Frost seemed to die on the operating table in "Death Falls." The Flash episode ended with the rest of Team Flash silently reacting to the bad news as Barry (Grant Gustin) and Caitlin emerged from the medical lab, unable to verbally confirm Frost's fate. Yet it appears Caitlin's tears said everything needed to be said, with Frost's boyfriend Mark "Chillblaine" Blaine (Jon Cor) taking the news the hardest.
The previews for the next episode of The Flash, titled "Funeral For a Friend," suggest that Frost's death is permanent. The upcoming episode summary mentions Team Flash grieving a fallen teammate while fighting a new metahuman bank robber. This would indicate that Frost will not suddenly recover, despite some suggestion her healing factor might kick in after her heart stopped. Sadly, while Frost's healing powers are incredibly potent, it seems that this will be one of the rare occasions a superhero's heroic sacrifice isn't immediately undone by the next chapter of The Flash.
The Flash releases new episodes on Wednesdays on The CW.