In Stargate SG-1 the Asgard seem to have all died either through the war with the replicators or when they blew up their planet, but in Stargate: Atlantis we see them again in their exosuits for two episodes, but I'm pretty sure that they also died.
But is there anyway that they could be alive? Maybe just a small group in the home galaxy or an outpost that is unaware of what has happened? Or anywhere for that matter. As they did have a break off group of researchers that were exiled, because of the research they were doing on there regeneration as they were clones could they still be alive?
Also the SGC has a device that can travel to different dimensions, why not use this to go to another universe and tell the Asgard there what had happened to the Asgard in their world, and see if they wanted to go back with them to rebuild their civilization?