I know we were a bit of a pain in the arse at times (though I'd say, no more than some other countries which doesn't seem to generate the same press or vitriol), but the EU would, in an ideal world, like us back. The chances of that happening are slim enough, swapping the £ for the euro would absolutely torpedo it.
That would probably be a good metric of how serious the will is for us to return, if the demands include losing our currency that to me would demonstrate that the talks are poisoned to fail.