Initial Thoughts on the Implications of the ECJ Ruling (short)

So it's official. The UK can unilaterally withdraw Article 50. What does this mean?

It somewhat increases the odds of a second referendum with a remain option on the ballot, as this is now a clear legal possibility. However, the political barriers to this are still sufficiently robust that this still seems unlikely. The timeframe of the Article 50 process also may not allow for a referendum to be held in time anyway.

However, it does have other, perhaps more significant implications. Firstly, it means that in the event that May's deal does not pass, and no deal is on the horizon, as the March deadline approaches, there will be significant pressure to simply revoke Article 50. This could plausibly be supported by MPs still advocating Brexit eventually, if they use it to argue that a better deal could be negotiated by a completely new process (the fact that this may be a political non-starter with the rEU won't matter, as few current MPs have ever taken such considerations seriously). It could also, at least hypothetically, increase the UK's bargaining position in the event that it sought to renegotiate with an Article 50 extension. If this were not granted, the government could threaten to rescind Article 50 altogether. It seems unlikely, however, that a May government would want to do this, due to the political damage of admitting its own previous failure, but it is not impossible, and we may of course have a new government rather soon. 

Potentially, and perversely, this could also somewhat increase the chances that May's deal passes. This is as some members of the ERG actively want there to be no deal, and have previously seen this as a likely consequence of May's deal failing. Now that this may no longer be perceived to be the case, they may feel they have to cut their losses and back the form of Brexit which is on the table. That said, game theory, or just thinking through the logic of outcomes has never been their strong point. 

Most importantly, as we are only talking about likelihoods and possibilities, there is a significant chance that in retrospect we will see this decision as having made no difference whatsoever, as the only outcome which could not have happened before anyway is one which may well not happen. But perhaps we will not.