Raiden. Just like in MK Trilogy.

The way you described the story of the movie happened in the game. Sindel had died, Shao Kahn made it possible to have her soul reborn on earth, giving him the power to step into the realm at his liesure.

Also in the game, (Mortal Kombat Trilogy to be exact), Raiden snatched Johnny's soul from the pergatory to make it possible to do battle again alongside earthrealm's warriors, just like Ninja_Mine says.

Will it be like this in the movie? Probably not, as much as they like to fuck up the story, like they did in the first two movies. Just know that he will return, but you might not understand or like how.

Armaggon, Ninja_Mime, Raiden only brought back Johnny Cage in MK4; in MK3/T, he came back because his path to the Heavens was blocked, so he just went back to his body on his own until Earthrealm and Outworld seperated. But odds are, yeah, Raiden will bring back Johnny Cage, unless the writers pull a Midway and either retcon Johnny Cage's death, or (what I'd prefer) they simply act like MKA never happened.

my guess is that its raideon, not becuase hes raiden but because he is an elder god, and the rules were broken resulting in johnys death, and the elder gods will undo whatever was done, im guessing its raiden because he is close to the humans, if he wasnt an elder god, another would do it