After having been reading up on the early period of the Troubles, specifically the suspension of the Northern Ireland government, I came to thinking about that act's validity.
The government was suspended (I think it followed Faulkner's resignation after he was unhappy that Westminster decided that the RUC should come under its control) in 1972. The original Treaty stated that only the Northern Ireland government should have the power to change the province's constitutional status. This was ratified further in other documents and official national and international agreements.
When Heath suspended the Northern Ireland government, it was only supposed to last for one year, until street violence was brought under control. But 1972 was the most violent year to that date and the British government applied a very soft approach to the violence - allowing it to fester. The very act of suspending the government was in itself a hint to the IRA that it had the kind of influence it sought.
My feeling is that the Northern Ireland government, which suspended in a not-entirely legal manner, is still merely under suspension... and that the British government could possibly appeal to the European or International bodies for the re-assertion of the Northern Ireland government.
Although this may not be desirable by many people, certainly it provokes interesting thought...