Unless May calls an election before 2019 then there is nothing Labour can do to influence Brexit. The Tories will just plough on without having a clue what it wants, broken into two camps, either scared secret remainers, or Brexiteers so driven by the ideology of Brexit, that even a UK turned into a tax haven and destroyed economically will be worth it.
The only course Labour can sensibly take is to remain a viable opposition, whilst pushing for a period of status quo transition, which is what it’s doing the last time I looked. Basically then, they are hoping to enter government with the deal still to be essentially made. That’s quite smart really, considering that the only pro’s to Brexit - being able to rewrite our own laws etc. so that they are more humane, or get through legislation for renationalisation of energy etc need a government that will not wreck the economy, i.e. take the investment approach over the austerity and tax haven approach.
The only chance this country has is for a Labour government IMO, and that means being smart. Hence, you don’t give the anti-Corbyn wing another platform to draw their knives, which is what happens if you debate Brexit at conference, and conference ends up deciding something either a) that the leadership doesn’t want, or b) something the voting public will despise, which given the nature of the issue would be any decision at all.
Conference just isn’t the place for the debate. Even Momentum falls out over Brexit. Why bother?