Read the story carefully:
Two ancient churches that once stood at the site of the current basilica were successively built over the spot where tradition said the saint had been buried. The second church, built by the Roman emperor Theodosius in the fourth century, left the tomb visible, first above ground and later in a crypt.
So the only thing that has happened is that 'tradition' has been reaffirmed.
The sarcophagus, which dates back to at least A.D. 390, has been the subject of an extended excavation that began in 2002 and was completed last month, the project's head said this week.
The sarcophagus is for real, but we don't know what or who is inside. Personally, I don't think it makes a difference if the contents are analyzed. If it turns out the sarcophagus gets 'debunked', people would still go there as if it were the real thing, just like they do with the shroud of Turin.