It would've transported Cedric to Little Hangleton by himself.
The Portkey was simply bewitched so that whoever touched it first would be transported to the graveyard at Little Hangleton. It didn't differentiate between different people; it would've worked regardless of whether it was Harry or Cedric who was touching it.
“He asked me whether I was ready to risk everything for him. I was ready. It was my dream, my greatest ambition, to serve him, to prove myself to him. He told me he needed to place a faithful servant at Hogwarts. A servant who would guide Harry Potter through the Triwizard Tournament without appearing to do so. A servant who would watch over Harry Potter. Ensure he reached the Triwizard Cup. Turn the cup into a Portkey, which would take the first person to touch it to my master."
(Goblet of Fire, Chapter 35, Veritaserum).
Clearly, Crouch Junior intended that Harry would touch the Cup first. His strategy, as the quote above shows, was to clear the way for Harry by attacking the other competitors from outside the maze. His goal was to get Harry to the Cup which he was successful in doing, even if he hadn't counted on Harry and Cedric helping each other out as much as they did. If Cedric had touched the Cup by himself then he would've been transported by himself and the plan would've failed.