Here is my answer:
First there are three North Americas and their “death” stories are different.
One includes the three countries and was never really born, except in the decaying value chains of the auto sector, whose relative weight for all three partners is declining.
The second includes Canada and the US: it is alive on security issues with NORAD and the new perimeter as anchors. Economically, it is getting weaker as its backbone, the auto sector, in spite of some revival, looks essentially doomed over the medium or long term as a core industrial activity. On the energy front, it is weakening too. With shale gas, the US is becoming more independent from us (and from Mexico too). Keystone is a detail, but it should push Canada to diversify markets in Asia, further exploding northern-North America. Now, it is not dead and won’t die, but its importance will decline.
The third one includes Mexico and the US. It is alive on security, on trade, on migration, but as both countries’ trade patterns diversify away from the region, it is weakening too. Not dead, not about to die, but declining.