Association agreements like the one between the EU and Ukraine require unanimous approval by all member countries. Britain would exit under different rules, so its deal might require approval from a qualified majority of the remaining EU countries. However, a decision to extend the 2-year time limit for negotiations – which seems likely to be needed – would have to be unanimous. So might the exit deal if it covered areas such as tax, foreign policy, and police cooperation. If the agreement covered areas where competence is shared between the EU and its member states, or the UK wanted Norway-type membership of the European Economic Area, that would also require ratification in all EU member states. A protest vote in the tiniest of EU countries could derail the process.This, to them, illustrates the unpredictability of a post-Brexit future. The thing is, we know all the risks of what would happen should we start opening up various cans of worms for negotiation. Hence why we would in all likelihood adopt the entire EU acquis warts and all, and not open up the various internal cooperation agreements for discussion.
Since many of the component cooperation agreements (Erasmus etc) have non-EU members, there is every possibility that these could be excluded from Article 50 negotiations. That much could be informally agreed before submitting our Article 50 notification. The talks are chiefly concerned with ending our membership of the EU entity without even looking at the peripherals.
The Commission and the Council of the EU hold consultations on the content and options for any upcoming negotiations. In most cases, the Commission starts an informal dialogue with the country concerned, which is known as a scoping exercise. This can cover the range and depth of topics that will be negotiated and is important to assess whether the countries have a similar enough interests for a deal to be feasible.
In order to minimise the risks, as discussed earlier, we would adopt an off the shelf solution with a view to not needing an extension. Given that we would not in the first instance be ending freedom of movement, nor withdrawing from the single market, that marks the least disruption for all and removes any moral justification or practical need for derailing the process.
Since the final vote is a qualified majority vote, it is reasonable to assume the deal would be ratified. Given the risks for both sides of such talks falling through, should any member use the opportunity for complicating matters they would find themselves leaned on by the others. Not forgetting we, as the fifth largest economy in the world do have some leverage in this.
Put simply, we would do everything possible to de-risk and simplify negotiations before even submitting our Article 50 notification to withdraw. This means very little changes immediately after leaving - and that's why all of InFacts's fearmongering amounts to silly histrionics.