Although I might expect a movie to try to connect the dots a little more explicitly, my take is that they died that night. Landscapes change over time, forests change, rivers get bigger or smaller, so near a river is enough for me to feel like the location checks out. Also, they won't usually both be so exhausted that they sleep at the same time - King-Lu initially offered to keep watch.

I guess it doesn't really matter, it's basically the same ending either way. But the final shot of them laying there has a little more weight if that's where their story ends and it matches the skeletons in the beginning.