[naturalman1975]

I don’t see how rebus sic stantibus involves the ECJ. It is an assertion of Britain’s sovereignty and places the EU and its institutions squarely outside in terms of influence. The ECJ is not the arbiter of all international treaties suddenly.

I'm not talking about the ECJ - since 2007 and the Treaty of Lisbon, the ECJ (European Court of Justice) is only one component of the JCEU (Court of Justice of the European Union). Another component - referred to as the General Court - is the relevant institution here. Under the terms of the Treaty of Lisbon, this General Court is the arbiter of European Union law, and of the Treaties of the European Union - that is actually its explicit purpose - Articles 263 is the most relevant here but a quick read makes me think Article 267 may also be relevant. All of Section Five is worth looking at.

Article 50 is dangerous. It cannot and will not guarantee that the UK is out without the EU causing damage to it.

No, but it will guarantee they are out. And that may be the more important guarantee in the circumstances.

[Olog-hai]

Article 50 cannot guarantee that the UK gets out, certainly not intact. Any exit on that basis is predicated on whatever the EU dictates to them as terms to get out, and that can damage the UK on the way out—which can reduce them to a vassal of the EU subject to their whims but on the periphery. Going the rebus sic stantibus route means that the EU cannot get a chance to act in this capacity. There is no trusting the EU treaties; the only sensible action is to render them invalid.