The broadcasters, represented by the so-called debate consortium, announced Thursday that they are going ahead with one English, and one French faceoff on Oct. 7 and 8.
The NDP, Liberals, Greens, and the Bloc Quebecois (only for the French debate), have agreed in principle to participate in the Ottawa event.
The Conservatives had turned down the consortium, and agreed to four other events.
Originally, it seemed that the network debate, to be shown on CBC/Radio-Canada, CTV, Global and Tele-Quebec, was on shaky ground without the prime minister.
But now that the NDP appears to have momentum in the polls, and Leader Tom Mulcair's own personal popularity is rising, the calculations are also in flux too.
NDP strategists in particular are evaluating the upsides and downsides of each of the many debates on offer.
In the absence of Harper, Mulcair could attempt to take on the frontrunner mantle — casting himself in the role of senior politician being challenged by the other party leaders.
The party is also keenly focused on building voter familiarity with Mulcair, and more debates rather than fewer theoretically helps. The consortium debates reached 10 million people in 2011.
"The 2015 Leaders’ Debates will have unprecedented reach, and will be offered across all platforms with closed captioning and simultaneous translation," reads the consortium press release.
"The debates will also be made available for other media outlets. As the negotiations with the invited parties' continue, the broadcasters maintain their invitation to the Conservative Party of Canada to participate in the televised debates."
During the French debate in particular, Harper would be potentially ceding key airtime in a province where the Conservatives are competing with the NDP and Bloc for seats.
The Conservatives have said they have one debate left to agree to, and it will be a French-language debate. That leaves the possibility that they will agree to participate in one of the consortium debates.
There is one glitch there, however. The French debate is scheduled on the same night as the NHL season opener between the Montreal Canadiens and the Toronto Maple Leafs, Oct. 7.
The English debate is scheduled for Oct. 8.
Other debates that the leaders are expected to participate in include one scheduled for Aug. 6, hosted by Maclean's Magazine and Rogers, and another hosted by the Globe and Mail on economic issues.