A vote of whom? Parliament? The people in a referendum?
Parliament
the recent ECJ ruling is somewhat ambiguous on PM vs parliament, that is down to UK constitutional law, which is always murky
I don't know why the ECJ would be involved, it is not the final arbiter over British constitutional law.
I suspect that politically the government would be well advised to get parliamentary approval for revocation, but I think legally they might not need to.
That is the nub of my question. If May can legally withdraw article 50 unilaterally and the only alternative is no deal, it is my opinion that she would do so, even at the cost of the downfall of the government. On the other hand, if she needs parliamentary approval to withdraw article 50, I think that might turn out to be as gridlocked as all the other votes and no deal will follow as it isa the current default.
Having said the above, if there has been a resolution that she cannot go for no deal (which I think there has, although I've really lost track of a lot of this stuff, so I might be imagining it), she could argue that there is no alternative but to withdraw article 50 and therefore she already has a parliamentary mandate.