The short of my opinion is that, yes, the NDP could easily win back these areas, however they'll win over urban Western Canadians, not rural ones.
But hey, while we're on the subject, what about us? Is it possible the Liberals could start winning in Western Canada, racking up huge majorities by appealing to the West's now-clear sense of centrism we've seen demonstrated in places like Alberta, BC, and Manitoba?
The short answer is... no. No, the Liberals are more or less dead in Western Canada, especially so in the rural areas of those provinces. That's a fact, and not even the collapse of the conservative option allowed us to make major headway in the West during the 1990's.
Winning the West has been a bugaboo of the so-called "Turner/Martin Liberals," or basically your business-oriented Liberals, who see the West as Canada's economic growth engine, and maybe even feel a kinship with the more business-friendly attitude espoused by most of the governments, past and present, in the West.
Unfortunately, any attempts to build up Liberal profiles in Western Canada have failed horribly. The last time we did have a significant, controlling presence (say, 30% of the seats) was in 1993; the last time we had the most seats was Trudeau's 1968 win. Aside from that one year, Conservatives or conservative-minded parties have controlled over 55% of the West's seats since the Diefenbaker era.
This makes the Liberal's prospects in Western Canada... slim, to say the least. Even the NDP could have a hard time holding the Conservatives below 60% of the seats, even with the current polling.
The Liberals, like the NDP, can only truly win in urban areas of the West. The problem for the Liberals is that in the most opposition-friendly cities - Vancouver, Edmonton, Regina, and Winnipeg - the NDP are the more natural choice of voters, given their history and their status as Official Opposition. You can also say that polarization has hit these cities fairly hard as well, and the choice is really seen as between the two, with the Liberals playing spoiler roles.
However, in those cities the Liberals do have their strengths. Universities, upper-middle-class areas, and the more suburban the city, the more likely individuals are to vote Liberal than they are New Democrat, if they'll vote for an opposition party at all.
That is why we power ahead in ridings like Vancouver Quadra or Calgary Northwest, but fall flat on our faces in ridings like Vancouver East or Winnipeg Centre. Are there enough ridings that are Liberal-friendly enough that we could grab a good number, say 20 seats, in Western Canada? Yes. But it requires that the Conservative option collapses first, and unfortunately that doesn't seem too likely in the near future.