The NDP would get torn apart by the national question in the context of the whole of Canada getting torn apart by the national question. But i think the chances of that happening are very remote. First of all the PQ has to win a majority in the next election under a very tarnished and unpopular leader - Pauline Marois. Then they will have to find a way to create "winning conditions" for a referendum some day in the future - which would probably take us into a hypothetical second term that they might not even win. Then there would have to be an issue of whether or not the referedum would even pass.
Its commonly accepted that if the Yes side loses in the next referendum - there will probably never be another referendum. Meaning that no PQ government will dare have a referendum unless they feel 99% sure of winning one - and i don't think those kinds of winning conditions will ever be there.
This is all so hypothetical its no even worth talking about.