About 5600 lines. However, because it was a glorified case statement, you were really only debugging a single case at a time, each of which was about the length of a sane function, so splitting it into functions would do little to improve readability. I like to trot out that example to terrify people, but the function itself was really quite sane and easy to maintain.
You did, however, have to fully understand the state machine as a whole, which in total was almost twenty kloc, had almost 200 instance variables in the state object, and leaned heavily on a tree object with about 30 instance variables. That's the point at which most people's heads exploded.
Either way, 4,500 lines is the size of a fairly straightforward iOS app. Most folks can dig into that and figure out enough to maintain it without spending a huge amount of time, even if the organization isn't ideal. When you hit tens of thousands of lines, that's where you have to start thinking about how you organize it and document it, because with such large projects, if you jump into the middle without a complete picture, you're likely to be hopelessly lost.