I think there is away back into the European Union. But, it won't be fast.
Labour can't block the exit. The debilitation of Brexit is not the facilitator of Labour's resurgence. Let's remember that in the English super-marginals we held in 2005, and then lost, the Brexit vote was nearly 60 per cent. But we can offer a safer surer route forward, if we accept the route needs to unfold slowly enough for the politics of Europe to gently bake a reform of free movement that we can live with, and adopt ourselves, sometime in the 2020s.
Here's my New Statesman piece with the argument in full: http://www.newstatesman.com/politics/uk/2017/03/slower-surer-road-back-europe