How do you think NI would vote if all the regional parties disbanded and the main parties ran there? If unionist = Conservative, then Conservatives would win a plurality, but it's not that simple.
Labour would win all seats except North Down and perhaps South Belfast and one or two others.
That rather depends on whether the hypothetical question is:
a) how would seats with the same demographic vote in England/Scotland/Wales (or, for the sake of controversy, the Republic)?, or
b) how would the same electorate respond to a forced choice between Lab/Con/Lib Dem?
For option a), the Tories would win North Down, Strangford, Lagan Valley and probably East L/Derry and North Antrim comfortably. Foyle, Belfast North, Belfast West and Upper Bann would be safe for Labour. Belfast East and East Antrim would be Labour in normal circumstances but with the Tories having a significant presence, South Antrim would be the reverse. Belfast South would be the sort of public-sector middle-class seat, once safely Tory, that the Lib Dems would have taken from Labour in 2005 or 2010. Of the more rural seats, West Tyrone and Newry/Armagh would most likely be Labour but the rest would probably go Lib Dem (although Fermanagh/South Tyrone would be marginal between Lib Dem and Tory).
For option b), "Unionist" voters would skew strongly Tory/UKIP, "Nationalist" voters strongly Labour. (The NILP had fifty years to develop a strong presence in working-class Protestant east Ulster and largely got nowhere except one or two seats in eastern Belfast.)
