On the 23rd of September Stephen Amell posted this photo below on social media that potentially suggest a death in either The Flash or Arrow.
Spoiler alerts everywhere!!!!
In this photo both Oliver and Barry are dressed in suits so it might be a funeral. For both characters to be at the same funeral it must be one of their “sidekicks". On an interview Danielle Panabaker (Kaitlyn) was talking about her character becoming Killer Frost in season 2 of The Flash. So my theory is this;
Captain Cold attacks them, freezing Kaitlyn until she dies. After the funeral, Team Flash realize that they need Kaitlyn back on the team for her intelligence, and they can’t cope with the loss of a fellow team member.
They try to bring her back by Cisco creating a machine to try to revive her however, it doesn’t thaw her heart and now when she touches anything she freezes it.
And that is why i believe that person will die.