Labour's policy on Brexit is very realistic. The country voted to opt out of the EU. The Party are following the wishes of the Leave voters, but in their own manner.
Corbyn and Labour want the final document to be voted on in Parliament. This will give MPs a chance to kick Brexit into the long grass. This is what Theresa 'SS' May is most scared of, hence her tedious no deal is better than a bad deal mantra.
Should this happen, Brexit could eventually be cancelled. The Referendum was advisory and not legally binding. Plus some Europeans are now saying Brexit doesn't have to happen, even though Article 50 has been invoked.
Corbyn and many in Labour are playing a smart long game over Brexit. No doubt the PLP backstabbers will start moaning about Labour not having a Brexit strategy. They'll probably team up with the Remain Tories ... just like the have on pfm funnily enough.
Jack