Okay, I just realized Voldemort didn’t just plan to kill Harry in Book 4
In all other cases except the Triwizard cup, portkeys only go one way at one specific time. Touching them again does not activate them to return to their place of origin. Also, when Harry grabs the cup a second time, it does not return him to the middle of the maze. It takes him to the entrance of the maze, in front of everyone.
Therefore, when Crouch Jr. (as Moody) bewitched the cup, he planned to have it take anyone who touched it first to the graveyard, then to the front of the maze.The cup was probably supposed to be a portkey to take the winner to the front of the maze anyway, so they wouldn’t have to try to fight their way out again.
Voldemort obviously planned to kill Harry. He had to. That was the whole point; to kill Harry in front of all his Death Eaters, all the ones who had deserted him and doubted his power to return.
There’s the possibility that he wanted to send Harry’s body back, either to divert suspicion somehow or to intentionally flout his victory in Dumbledore’s face. Except Voldemort had promised his precious Nagini several times she could eat Harry, and it seemed like a promise Voldemort was going to keep.
So who was meant to take that return trip?