Managed to get virtually to the end. Was probably a few seconds away from the helicopter site. Character got to a point where there was a long jump down, glitches into the wall and then the game immediately saved.
Come to find out that not only did the game save my character while trapped in the wall but it also had only been using one auto save slot the entire time I'd been playing.
Not willing to go through all the same convo again so I guess I'll just never finish it.
What a waste of money. Thanks developers!