The question is a bit vague, inasmuch as it does not specify who was doing the planning.

On the side of the PQ, the notion of Québec partition was simply deemed untenable, and that international law was a sufficient garantee against it (source).

However, at the federal level, the opposite was at least considered. For instance the PM at the time was quoted as stating that if Canada was partitionable, it followed that it must also be the case for Québec (Charron, Claude G., La partition du Québec: De Lord Durham a Stéphane Dion. (Montreal: vlb éditeur), 1996, p. 167.)

Meanwhile, the Inuit themselves wanted nothing to do with a sovereign Québec, and said so through some of their chief negociators, such as Zebedee Nungak and Charlie Watts. For one thing, they worried about losing their ties with the Federal government and with other Inuit in the rest of the canadian arctic (source). Furthermore, the Inuit had long-lived concerns that the Federal responsibility to consult them as aboriginal people was steadily eroding, as witnessed by the fact that they had not been consulted when Nunavik was transferred to Québec in 1912 (source). The also saw the prospect of being excluded from their (relatively) new Canadian identity into yet another new country through a referendum where their voices would not matter (through sheer demographic weight) as going against their own aspirations to self-determination (ibid.). As witnessed from political cartoons of the time (see: From Eskimo to Inuit in 40 Years, 2011, published by Inuit Tapiriit Kanatami, p.78), passage to a sovereign Québec was also seen as fraught with the risk of forced cultural assimilation. One such image, for instance, shows a lone Inuk facing René Lévesque backed by marching ranks of language police bearing the “bill 101” standard.

Although OP did not ask about other aboriginal nations, the Cree (for instance) were also very vocally opposed to remaining within a sovering Québec and would have sought partition as well, using arguments similar to those voiced by Pierre Trudeau (see p. 50 source "Coon Come souligne que le Québec revendique le droit historique de déterminer son avenir sur la base d'une langue, d'une histoire et d'une culture distinctes. Comment, demande-t-il alors, le Québec peut-il affirmer que ce droit ne s'applique pas aux Cris? Les Cris n'ont-ils pas de langue, d'histoire et de culture distinctes?")

How does it all add up? As far as can be inferred from existing sources, a newly independent Québec would have had to defend its territorial integrity to a refractory Canadian Government backed by a local population which felt more attachment to its Canadian identity and wished to preserve its territorial integrity while pushing for its own self-determination. Can any of this be called a plan though? A recent book on the 1995 referendum recent book on the 1995 referendum showed that neither the yes side nor the no side had a coherent and well thought out strategy for dealing with “Day 1” after a “Yes” vote (I hope I'm not violating the 20 year rule by referring to such recent work). One may perhaps surmise that such was also the case in 1980, and that a “Yes” would have been followed by unforeseen chaos and partisan infighting.

EDIT: Also worth mentionning that the James Bay Agreement does not simply "give the Inuit control over the northern third of the province" as OP suggests. It gives them ownership of some lands (Cat 1), and codifies their right over hunting and fishing in Cat 2 and Cat 3 lands. It also sets the basis for the regional political and administrative structures. We are a far cry here from Inuit governmental autonomy.

David Varty notes that the northern 2/3, Ungava, actually belong to the inuit of Canada and would more than likely be given to them in the event of separation, as Quebecois stewardship of these lands would be illegal as the agreement was made between Canada and the Inuit on behalf of Quebec. Quebec's borders would look quite similar to the province at the time of confederation. This however was rarely brought up in the first separatist movement as it was more a case of preserving the country against what was viewed as a radical extremist group that did not have a large chance of success, as opposed to round two and the more peaceful and palatable (from a democratic standpoint) attempt at separation.

Because agreements with first nations are made between the federal government on behalf of the provinces all native land is held in trust by the crown, giving provinces like British Colombia a sizable reason to not secede without further clarification on the issues of crown land allocations and treaty rights.

Also worthy to note that separatism is at an all time low in Canada (it has been strong from varying regions for most of history) and current movements are towards global integration on a supra national level, not the devolution of power here in Canada.