It may be theoretically possible to reverse article 50 but Teribus is correct. Once Article 50 is triggered we're coming out. There will be no political will, or bravery, to reverse the thing either here or, especially, in the other major EU countries, who do not want to see anyone pissing around with this lest it triggers a landslide. If there's a fight to be had at all, it will have to be before Article 50 is triggered. Realpolitik, je pense.