Just because the wedding will be a disaster doesnt mean Barney and Robbin wont get married. Marshall and Lily's wedding was a disaster too. We know it rains on their wedding day so that alone hints there will be problems. That also fits into the theory I have that Marshall will dole out the final slaps in the series finale. That wont make for a very happy wedding day foe Barney.
I'm starting to wonder if Victoria will actually be the Mother. If they break up again, and meet miraculously again at Barneys wedding, Ter can tell the kids "and that is how I met your mother... And then met her again... And again... And one last time."