Took me months to complete for the same reason as yourself. The save system works very well. It seemed that every little bit of significant progress was saved.Im thinking of getting dying light but don't have a vast amounts of time due to kids...what's save system like, can you jump in and out?
In addition to this when the level loads, when you come back to it, you are read a sentence that summarises what the plot is. So if you come back to it a couple of weeks later you know what is going on.
I made a point of completing this one and although I rushed through the end, I really enjoyed it.