The Liberal Party went from Government to obscurity in a decade or so. No reason why that cannot happen with Labour.
Perhaps as part of the wider conversation it needs to be in the mix that not only could that happen but that perhaps it isnt the end of the world if it does? perhaps a new centre left political party made up of libs and more moderate labour and a more radical left wing option is actually a better fit for Labour and indeed the current uk political spectrum
Brexit ..............Conservative..........social (or Eropean) democrats ............momentum
(Far right) .......(centre right)..........(centre left lib + centrist Labour) .........(far left - possibly with greens?)
that might actually be a better model if it becomes apparent that Labour is too focused on internal battles
Brexit will need to rename themselves, the centre left party would as well - momentum could keep the labour name I guess
under a PR system the two wings of the party would most probably be different parties already and then the focus would be collaborative and how they can work together - As one party the fight is to control one unified policy.
Ironically if there was a split it could well result in 3 of the main 4 groupings (far right, Centre left and far left) all wanting a PR system which ultimately would probably be more collaborative in the long term... as it stands though I dont think either wing of the party os prepared to give up the name recognition and funding or at least not without one last fight
i do understand that there has been some informal talks about a new centre left coalition that predated the change uk move... might actually come to fruition if we end up with a bailey burgon type arrangement in labour
Either way it wont be the end of centre left or indeed far left political activism in the UK - and actually unless somebody can unify the Labour party (and I dont see anybody that can at the moment) it might actually be for the best in the long run