Yes they are a very resilient organisation.
It's hard with Labour though, as frankly there is a group of people, who a particular ideological wing of the party who are unhappy to be anything other than in charge. If they are not in charge, they look to sabotage from within. It's very hard to forgive that behaviour. It's sort of like if you were playing a football match, you'd dislike your opponent, but probably dislike someone a lot more if he started scoring own goals and deliberately helping your opponent unless they got to becaptain and take the penalties. Now they are back being captain and going on about how rubbish we were when we lost (largely due to their own goals) and also the need for unity. It sticks in the throat a bit.
As for the left, for the most part it is clueless on power and you are right to say doesn't think enough in those terms. You have lots of people on the left, who are still desperately trying to tell people to stay in Labour to recapture it, with seemingly no real analysis or understanding of why it failed last time? Say they are successful again (which they/we won't be) what is going to stop it being exactly the same result again?
I'll be frank, I don't think there will ever be a successful left led Labour party. People point to Atlee, but he himself wasn't a massive left winger, he just existed in times where the argument had shifted. The Labour Party is not going to magivally become a Syriza/Left Bloc/Die Linke type "party of protest" (to coin Paul Masons phrases before he dropped that idea for the next bandwagon to jump on).
I am quite relaxed about Labour. If people won't want to vote for Labour, thats up to them. Personally I will, but I understand why you wouldn't. I think the bigger mistake in this context though, is to go ploughing endless energy into an organisation in the hope you might one day run it. I mean if people want to do it, again good luck to them, but the alleged intellectual leaders are just leading people down a trap. You either make peace that you are helping what will always be a fairly moderate party who will govern for the rich at times of crisis (with a few more crumbs being given out to the rest) or you havw a way of squring the contradictions above that I can't see.
I should add, it is possible to look to build an alternative on the ground, but also vote for Labour in the short/medium term. It'sa bit of a grubby approach, but the politics of purity doesn't get us so far. We need to have a more honest, and at times self serving relationship with Labour in my view.