McGuinness quits - what happens next?
Once Martin McGuinness' resignation takes effect, under the joint protocols that govern Stormont's power sharing government, First Minister Arlene Foster also loses her office.
She may continue to exercise some functions, but her role will be very limited.
Sinn Féin has seven days to re-nominate a new deputy first minister following Mr McGuinness' resignation.
However, the party is adamant it will not replace him.
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From the evening of Monday 16 January, the baton passes to Northern Ireland Secretary James Brokenshire. The law says he shall call an election.
The usual time period for an Assembly election campaign is six weeks. If Mr Brokenshire moved immediately, then voters in Northern Ireland would be going to the polls in seven weeks' time.
However, a previous court case indicated that the Northern Ireland Secretary did not necessarily need to call an Assembly election immediately, but within a reasonable period of time.
Mr Brokenshire could use this flexibility to allow for more negotiations.
What he cannot do as the law stands is suspend the Stormont Assembly and Executive.
That power was used by previous governments on a number of occasions, but it was removed from the statute book as part of the 2006 St Andrew's Agreement.
It would require a fresh emergency law to be passed by Westminster for suspension to be used again in the future.
During the 2015 crisis over welfare reform and IRA activity, the Northern Ireland Office was adamant that, in the event of a breakdown, it would not try to bring back suspension powers, but allow fresh elections to take place.
Government sources indicate that thinking has not changed, even though a potentially polarising campaign might not make the restoration of devolution in spring any easier.
Sinn Féin say their rift with the DUP is far wider than the latest Renewable Heat Incentive scandal.
But whilst the Stormont parties go into election mode, it seems unlikely there will be any progress on either recouping the potential RHI losses, or agreeing an independent investigation into the affair.