A past version of Captain Cold tuned up in the Legends of Tomorrow Season 1 finale, and showrunner Marc Guggenheim teased that the rogue would have a presence in Season 2.
Throw in the fact that the Legion of Doom band of villains was stated to include Captain Cold, and it was inevitable that he’d pun his way back to prominence.
The question was just of when.
We already knew that Captain Cold would be back in an important way at some point, since it was announced shortly after the character’s death that Wentworth Miller had signed on to The CW’s DC universe as a regular who would visit Arrow and The Flash as well as Legends of Tomorrow in the 2016-2017 TV season.