Насколько я понимаю, согласно Lisbon Treaty, статья 50 дает возможность вести эти переговоры только 2 года со дня уведомления, потом все договоры умирают.
The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.
no subject
Date: 2016-06-25 04:05 pm (UTC)The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.
http://www.lisbon-treaty.org/wcm/the-lisbon-treaty/treaty-on-European-union-and-comments/title-6-final-provisions/137-article-50.html
(The Lisbon Treaty was drafted as a replacement for the Constitutional Treaty which was rejected by French and Dutch voters in 2005.)