Looks like the EU court will rule that the UK can revoke Article 50 without the permission of the wider EU:
https://twitter.com/bbclaurak/status...68636368715776
Unlikely to be needed but in the event of a second referendum the fact the UK may be able to simply revoke it rather than ask permission would mean , again in theory, that the EU can't impose conditions such as losing the rebate on such a decision.