WINston no longer has the, as newshub put in on election day, 'moral obligation' to join up with English, considering there is only a 2 seat difference between Nats, and Labour-Greens, and the party vote is within a point or so.
In what universe does one add the Labour and Green votes and seats, but, one does not add the National and ACT votes and seats?
There is a 10 seat difference Labour and Nationals. There is a 12 seat difference between National-ACT-NZF and Labour-Green. There is a six seat difference between Labour-Green-NZF and National-ACT. Does a 12-seat majority have a greater "moral" mandate than a 6-seat majority? Probably, it does under some moral theories [the significant plurality {10-seat} party ought to have the first shot at forming the government,] but, not under others [Aside from siding with hostile nationals directly at war with New Zealand, or soliciting graft or other illegal behavior, elected officials are free to take any decision they wish for any reason they choose, or for no reason at all.]
Personally, I have always subscribed to latter moral theory. If Peters hasn't promised the electorate to support either party, it is purely his call.
Of course, four members of NZF could break away from a Peter's decision to go with Labour, or six members could break away from a National agreement.