The reality is Labour will suffer its worst ever election defeat in 2020, Corbyn & co will resign and Labour will elect another Blair type figure anyway, because like it or not, in 21st century Britain, you will only win power from the centre.
By 2025 we will have had a wasted 15yrs of navel gazing and student union protest politics from Labour and a betrayal of those most in need of a Labour government, offering up a candidate with no chance of winning is not a real choice, its just cowardice.
If Corbyn supporters really believe a terrorist sympathising, unilateral disarmer candidate stands a cat in hells chance of being elected, they need to go home, take their clothes off and pull their heads out of their arses and stop talking the kind of naive shit that only fellow believers agree with.