Sinn Féin did not take their seats in order to keep the DUP out of Government while putting Jeremy Corbyn and John McDonnell in. They are certainly not going to bother in order to block the best chance of a United Ireland since Partition itself.
The EU's proposal for Northern Ireland ought to be put to a referendum there. Perhaps along with same-sex marriage, and the proposed Irish Language Act. That would be quite a questionnaire. But even by the standards of that territory, these are not normal times.