The
European Court of Justice has ruled that it would be legal for the UK to unilaterally revoke Article 50 to cancel Brexit (without the need for agreement from the other 27 EU countries).
With the government still committed to Brexit, it's very likely that a major event such as a further referendum or change of government would have to happen before such a move.
However, any delay to Brexit would certainly lead to questions about whether the ultimate destination was going to be a reversal of the 2016 referendum.
It's not totally clear what the process would be. But an act of Parliament calling for Article 50 to be revoked would probably be sufficient.