Yes, this is their one ‘legitimate’ play to stop Brexit. If Labor decided to make this a ‘pseudo-referendum’ on it (unlikely, I think, but not impossible) and won (very unlikely) a legitimate constitutional case could be made that ‘the people have spoken and changed their mind’.
Of course, this would also require the EU nations to agree to allow Britain to back down.
So it could be very interesting.
I can’t really see it happening, but I can certainly see people trying to make it happen.