"Restoring a sustainable and fully functioning devolved government will remain our goal but we will not accept a one-sided deal", said Foster, who as recently as Friday noted that the parties had made progress in the talks.
Around 2,000 delegates are expected to gather at the conference for the ratification of Mrs McDonald as the next party president.
Talks to restore Northern Ireland's collapsed government have failed after weeks of intense talks, the leader of the region's major Protestant party said Wednesday.
She said her leadership would mark a defining chapter in the achievement of a United Ireland.
Mary Lou McDonald, the new Sinn Fein leader, said that the two sides were close to an agreement.
She also ruled out any laws that would require bilingual road signs in Northern Ireland; compulsory teaching of Irish in schools; or quotas of Irish language speakers within the civil service.
However, speculation has been growing that a deal between Sinn Fein and the DUP is close.
There was no breakthrough in talks to resolve Northern Ireland's 13-month power-sharing impasse on Monday, despite Irish Prime Minister Leo Varadkar and British Prime Minister Theresa May visiting Belfast to meet the territory's political leaders.
Missing Toronto firefighter found in California
One employee at the mountain jokingly said in passing Tuesday, "Whiteface is now home to the longest ski trail in the world". Deputies said Filippidis bought a cellphone at some point along the way to California, but he doesn't remember where.
Update 2.31pm: It is unlikely a power-sharing deal for Northern Ireland will be decided today.
'However they want to describe it, the DUP know that agreement requires an Acht Gaeilge. If that embarrasses the British prime minister, then so be it.
The DUP/Sinn Fein-led coalition imploded last January amid a row over a botched green energy scheme.
Sinn Fein demands for Irish-language protections emerged as the main sticking point.
Since the March 2017 election, Irish nationalists and pro-British unionists were unable to find common ground on divisive issues such as the Irish language act and legacy issues inherited from decades of violence popularly known as the Troubles.
The Sinn Fein leader acknowledged "we are not exactly there just yet", but "there is nothing insurmountable if there is the political will to reach an agreement".
Mr Eastwood said it is not enough to simply form a new executive.
But while such hopes proved unfounded, all parties said an accord was in sight.