I'm so sorry your chick died! It wasn't your fault though. I would've helped if I were you, too. In fact, I did - I had 3 chicks in this year's hatch that had the same problem - started zipping but couldn't finish, and started drying out. I helped all 3 of them. Once they start zipping, it's safe to help because it means they've absorbed the yolk and the veins have receded, so there's no danger of bleeding out. Helping at that stage is low risk, but can really up their chances of survival, and if you don't intervene, they can die because the membrane eventually dries out completely (even with high humidity in the incubator) and gets glued to them hard, restricting their movement and locking them in the egg. Gently cleaning the shell and membrane off with a warm moist cloth is exactly the way to go, just like you did. Mine were really glued down. All three of them made it out alive. However, two of them had problems and the third is still a runt, 1 month later. One of the problem chicks had severe wry neck and breathing problems and died, and the other had problems with its eyes. It's very likely that the chicks failed to hatch properly because there was something else wrong with them already, and that something is likely the reason why yours died - not something you did (or didn't). Like with my chick - it died because it had underlying problems - the wry neck and breathing problems - not because of the hatching issue. So, if you end up in this situation again, at this particular stage of the hatch, absolutely do help - it could save a life, and if the life is lost anyway, then it won't be your fault, but would've happened anyway. 2 of my 3 assists from this year are still alive and doing very well 1 month later, and even the chick with the eye problem has adapted and is a robust little cockerel right now.