They had to have done something different at some point or they would not have been able to move on. If what you’re saying is it’s one big continual loop that happens over and over= plane crash -events-detonating jughead in1977- plane crash- events- detonating jughead in 1977- plane crash….what do you think was different in order for them to finally move on in the finale? I mean, they didn’t move on and ‘go into the light’ …..and then board flight 815 again and it all started over again…..
they let go, move on, go into the light and get to live happily ever after (paradise, heaven, fields of light, reincarnation etc…) time is not a loop, time in linear in LOST. It simply happens that some of the casaways “straight line” involved a detour in 1977.