Theseus was a great Greek hero who had already accomplished many amazing things up to this point. Although the maze was known for constantly shifting around and never having a clear path, some of the human sacrifices that are thrown in there have found their way to the center and also the Minotaur. Of course, the Minotaur just kills all of them. I believe Ariadne's string was just a faster, sure way of reaching the center. Because Theseus would have been able to best the Minotaur, the biggest challenge was getting to the middle. So it would have been likely that Theseus could still have found his way.
