Parties must convene and decide how to avoid a no deal Brexit. Together, if possible. Whatever BJ says, that's the case.
McHrozni
The problem is that the Conservatives and Brexit Party actively want a no-deal Brexit.
Jeremy Corbyn seems to prefer a no-deal Brexit to no Brexit - my guess is that he thinks he can negotiate a great deal after both the EU and UK have suffered the consequences of a no-deal Brexit
So while in a sane world they should do exactly what you say, Brexit seems to exert a bizarre influence over politicians and they seem mesmerised by 20% or so of the population.