Extending the deadline requires unanimous vote, which, since enlargement to 28 countries, is basically impossible. The interpretation of paragraphs describing art.50 triggering is vague enough that the EU will find ways to trigger it themselves -- it's already been suggested that a speech taking place in an EU setting and getting transcribed will be enough, which means UK diplomats and ministers are now all but ostracized from formal meetings of any sort outside the negotiation process.

There is no way this situation can extend for 10 years. The EU will not allow it, especially if recession hits. If really UK elites get cold feet, we'll have a general election with an europhile party winning and abandoning the whole thing, with a second referendum forced.