First and foremost, before I entertain this question, let me be quite clear in that I do not
think that the H5N1 virus is going to cause anything near, or even in the same arena as, the collapse of governance to any serious degree. I don't think there is a chance of that happening.
Nonetheless, to deal with the question at hand, no, I don't think that people would go into a tribal system
. I think that people (in Canada, at least) would be somewhat lost with the collapse of the Government of Canada
and the Governments of the Provinces
I think that people would continue to follow whatever the nearest source of authority would be (whether that would be the province's government, in whatever state that would be in, or a municipal authority of some sort); furthermore, I think that people would be awaiting, with some anxiety, the "return to power," if you will, of the Government.
Nonetheless, as I mentioned above, I highly doubt such a situation would ever occur.