The future of the Labour Party, whatever happens, is deeply uncertain because this is such a profoundly right-wing age and it is really debatable what role a centre-left party can play in it. This isn't unique to Britain but has happened all over Europe as
"Pasokification" (named after the collapse of the Greek centre-left party). So it is really anyone's guess what Labour will do now.
Being cynical, he's probably going to try and consolidate his base within the party and ensure that his successor will continue his policies. They probably don't want Labour to go to the right/move back to the centre (where ever that is now). If the Labour Party tried moving to the right, it would only consolidate Johnson's victory by ensuring Labour surrenders to Johnson's policy positions. Basically, they need to make sure a Labour civil war doesn't turn in to a major split between the centrist and centre-left factions.
Personally, I'm genuinely at a loss to know what the options even are for centre-left/far-left politics now as we have basically gone further and further to the right since the 1980's. Johnson's win is simply a continuation and exaggeration of that process. So who the **** knows?