Michelle O’Neill and Mary Lou McDonald strode into the Magherafelt count centre on Saturday like republican royalty trailing a retinue of cheering admirers and activists, all eager to bask in this moment of Sinn Féin’s triumph. A road that arguably started in 1981, when the IRA hunger striker Bobby Sands won a Westminster seat and set the party on an electoral path, led to this cavernous sports arena in County Derry, when the party that wants to abolish Northern Ireland became its biggest party. The Armalites long discarded, it was the ballot box alone that gave Sinn Féin victory in the assembly election. Francie Molloy, Sinn Féin’s MP for Mid Ulster, and a veteran activist, soaked up the scenes of rapture. “A lifetime waiting on this day,” he said. “It’s been a big change. Now we need to build what future Ireland will like.” O’Neill, the party’s deputy leader and designated first minister, immediately sought to calm those who fear the Sinn Féin victory will hasten the region’s exit from the UK and promised to focus on bread-and-butter concerns. However, she made a coded reference to the party’s push for a referendum on a united Ireland. “Today ushers in a new era, which I believe presents us all with an opportunity to reimagine relationships in this society,” she said. Asked for her message to unionism, McDonald, the party’s leader, replied: “Don’t be scared. The future is bright for all of us.” McDonald leads the opposition in the Dublin parliament and is widely seen as a taoiseach in waiting. As counting continued for the allocation of final seats, it was clear that Sinn Féin, with 29% first preference votes, had overtaken the DUP, which won 21.3%, with two seats between them on Saturday afternoon. It meant the all-Ireland republican party would be entitled to nominate O’Neill as Northern Ireland’s first nationalist first minister. Taking to the podium to accept the formal declaration for the Mid Ulster constituency, O’Neill was distinctly non-triumphalist, promising to work for all sides. “My commitment is to make politics work. My commitment is to work through partnership, not division. People demand cooperation, people demand delivery,” she said, urging the DUP to “turn up for work on Monday” and put aside their protests about the Brexit protocol for now. “There is an urgency to restore an executive to start to put money back in people’s pockets, to start to fix the health service,” she said to hordes of press and a phalanx of Sinn Féin supporters. The scale of the party’s victory left unionists at some count centres visibly stunned. While the unionist vote was split three ways, it was “not utterly catastrophic for the DUP”, said Jon Tonge, professor of politics at Liverpool University. But he added their “crown is lost” as they now must face an assembly where they will be the second-largest party in the mandatory power-sharing coalition. It was a sobering day for Doug Beattie, the leader of the Ulster Unionist party, who scraped in on the seventh count after offering a more liberal and progressive programme, which he believed would appeal to an emerging cohort of secular unionists less interested in the politics of green versus orange. Those votes were siphoned off to the Alliance party, the other big winner in Thursday’s election, which jumped to 13.5% of first preferences and looked likely to double its previous total of eight seats. Those gains were largely at the expense of the UUP, the moderate nationalist Social Democratic and Labour party (SDLP), which haemorrhaged support, and the Green party, whose leader, Clare Bailey, lost her seat. “It’s the Alliance hurricane,” said one party activist. The “baby of the house”, Eóin Tennyson, 23, the youngest elected MLA and the first ever Alliance representative for Upper Bann, captured the moment as he choked up making his first speech as an MLA. “I’ve always been told the politics in Northern Ireland … would always be orange and green. I think that we have smashed that narrative,” he said. “I don’t really like the unionists or the nationalists. I’d like to see a party for Northern Ireland, not for division,” said first-time voter and engineering student Natasha Nesbitt, 19. “I feel Northern Ireland is quite behind on issues like abortion. I hope when my generation are older, Sinn Féin and the DUP will go down and others will go up.” Under power-sharing rules in the Good Friday Agreement, Sinn Féin, the DUP and Alliance, and possibly other parties that may clear a threshold, have eight days to form a new executive – but they have up to 24 weeks to do so under new laws signed off in Westminster. The DUP leader, Sir Jeffrey Donaldson, has already made the party’s position clear – it will not enter an executive until the protocol, the post-Brexit deal that puts a trade border in the Irish Sea, is reformed. It, in effect, puts Boris Johnson on notice: Stormont or the protocol. Without a first minister and deputy first minister, the executive cannot function fully, with ministers limited to continuing but not making new policy, and not able to sign off budgets or introduce much needed health reforms. Senior DUP sources said they will seek an urgent summit with Downing Street to press home the message their boycott can put the assembly on pause until Christmas. If no executive is formed the Northern Ireland secretary must call a new election, which in turn must be held within 12 weeks, pushing the chances of a full devolved government back to December. The DUP also faces another urgent dilemma. After a ban on double-jobbing, Donaldson will have to decide if he is to remain as an MP or take up his new seat as an MLA and force a byelection for Westminster.