Probably, the journalist said to the protestor "When are you going to stop protesting?" or "Are you ever going to stop protesting?", or even "What would it take for you to stop protesting?" - something of that ilk.
The response would have been "We're not going to, until Morsi is restored to president and democracy is restored to Egypt." But it would have made no sense to quote this, without adding the part in square brackets.
As a general rule, square brackets indicate something that's been added to a quotation, that wasn't what was originally said.