SF will find it very difficult to surge past DUP without their former 'bogey man'
It is strange to think now, but at the start of the North's 'peace process' Martin McGuinness was a 'bogey man' who both governments thought was diametrically opposed to an IRA ceasefire never mind Sinn Féin's entry into Stormont.
"McGuinness is against it," was a fairly commonly used term. It took nearly 10 years for Mr McGuinness to be 'for it' and then in a way that surprised many as he sidled affably into government alongside Ian Paisley.
Gardaí who knew Mr McGuinness and what he did in the IRA said all along that there could be no deal without him.
He was the leader, these sources said, and mention of his name instilled fear across the IRA.
Gerry Adams held sway in Belfast and across the political movement but Mr McGuinness, who admitted his membership of the IRA but lied about leaving in the mid-1970s, was the figure needed to move the Provos from 'war' to 'peace'.
His role has been crucial in both working the settlement in Northern Ireland and also leading Sinn Féin and the IRA as an undivided movement even with the disappearance south of Mr Adams.
Republican sources in the North yesterday said Sinn Féin has reached a critical juncture with Mr McGuinness's departure.
There is no other figure of his stature in the party in the North and the appointment of a successor may be fraught with problems.
There is no obvious heir apparent.
Sources point to a number of likely figures, all with pros and cons but none with the political abilities of Martin McGuinness.
Few of those possible replacements are commonly known across the Border. South Armagh's Conor Murphy is one leading contender.
But there are said to be internal pressures mitigating against his stepping into Mr McGuinness's shoes, particularly from the increasingly influential non-IRA members of Sinn Féin who see a need to put a distance between themselves and the type of damaging re-appearances of victims of IRA murders and atrocities.
Another figure emerging in the race is Michelle O'Neill, from Dungannon, Co Tyrone, who served as minister for agriculture in the assembly from 2011.
She is seen by some as presenting the new, less extreme image of the party that has nearly been achieved in the Republic.
Mr Murphy and Ms O'Neill, however, are likely to face competition from the party's national chairman, Declan Kearney, from north Antrim.
He is the 'architect' of the party's North and South strategies.
And he is the person who has made most of the key organisational changes that have moved the party into a nearly unassailable position in the nationalist community in the North.
A fourth figure who may yet come to the fore in the North is Máirtín Ó Muilleoir from west Belfast, currently the North's minister for finance. He is seen in west Belfast as Mr Adams's chosen successor, whether that is true or not, it seems most generally agree Mr Ó Muilleoir has a better public image than Mr Kearney, who is often seen as distant and aloof from 'ordinary' politics.
While the view being held yesterday was that the resignation of Mr McGuinness need not necessarily prompt an election, there were indications from Sinn Féin sources that a snap election is their preferred option.
The reasons are tied to the party's near completion of its upwards trajectory in Northern Ireland and the prospect of a possible and irreversible decline.
In the last assembly election in May, SF was stunned by the first-past-the-post victory of People Before Profit candidate Gerry Carroll (29), gaining 8,299 votes and stripping nearly 7,000 votes from Sinn Féin in its west-Belfast heartland.
Veteran socialist Eamonn McCann's election in Derry, also on a People Before Profit ticket, added to that shock.
With the reduction in assembly seats from 108 to 90, a snap election allows Sinn Féin the tantalising opportunity of running for an all-out victory, surpassing a DUP embroiled in financial scandal over 'renewable' energy payments to supporters, to become the biggest single party and therefore hold the position of first minister in Stormont.
That may be very difficult without a Martin McGuinness.