If something big enough comes around that they do consider confiscating weapons, I think chances are they're going to be too busy trying to deal with it to actually do the confiscation.
I mean, seriously, they only got around to trying in New Orleans after things had calmed down, and it seemed like they were only doing it to try to convince people who had stayed to leave.
IF they wanted to try it on a national level, they would have to do a thorough search of every residence in the country. If you know they're on the way, what's to stop you from sneaking a few off somewhere else? National gun confiscation would be a Sisyphean task.
There would probably be considerable uproar over wasting resources to round up guns instead of dealing with whatever disaster convinced them it might be a good idea.