If the DUP and Sinn Fein are returned as the two largest parties after an election, but their row is unresolved, it is unlikely that a new ruling Executive could be formed.
That raises the real prospect of the devolved power-sharing institutions being suspended and a return to direct rule from Westminster.
Suspension of the Assembly was an all-too familiar feature in the years after the Good Friday peace agreement of 1998:
February 2000: Secretary of State Peter Mandelson suspends the Assembly after the UUP/SDLP-led Executive fails to strike a deal on IRA decommissioning. The institutions are restored in May after the IRA pledges to "completely and verifiably" put its arsenal beyond use.
August 2001: In the absence of progress on decommissioning, Northern Ireland Secretary John Reid suspends devolution for 24 hours - a manoeuvre that effectively gave the parties a six-week period to find a way forward.
September 2001: With the IRA having pledged to intensify engagement with an international panel set up to monitor decommissioning, Mr Reid triggers another technical 24-hour suspension to give the parties further breathing room.
October 2002: Sinn Fein's offices at Stormont are raided by the police as part of an investigation into an alleged IRA spy ring at the heart of Government. A major political crisis erupts and, 10 days later, Mr Reid suspends devolution and announces the return of direct rule. London-based ministers would retain control of running Executive departments until 2007 when the then DUP leader Dr Ian Paisley and Sinn Fein veteran Martin McGuinness entered power together.