Today [9th Jan 2017] it was announced that Martin McGuinness will be resigning from is position as Deputy First Minister of Northern Ireland. (Source)
Martin McGuinness is the leader of Sinn Fein, the second largest party in Northern Ireland and the joint head of the executive (governing) branch along with the leader of the largest Northern Irish party, the Democratic Unionist Party (DUP), First Minister Arlene Foster. It should be noted that under the Good Friday Agreement (GFA), there is no formal seniority between these two roles, and the designation of ‘First Minister’ and ‘Deputy First Minister’ are designated based on the largest party and second largest party within the Northern Ireland Assembly respectively. The two governing parties share executive power under the GFA.
The resignation of the Deputy First Minister therefore signifies a threat to the overall stability of the Northern Irish Executive, with Sinn Fein ruling out a replacement for the post, whilst calling for the resignation of First Minister Arlene Foster. The reasons for both of these acts is based around the Renewable Heat Initiative (RHI), of which failings Sinn Fein holds the DUP and Arlene Foster accountable.
The resignation and continued position of Sinn Fein mean a snap assembly election is highly likely given they will not offer a replacement within the required seven days. Arlene Foster also technically loses her role as First Minister given the need for there to be someone in both posts for the executive to function under the GFA.
The result of an election is also likely to reset the relations between the two parties negotiating positions, meaning that concessions on either side may need to be fulfilled for a peaceful transition to be established.