Wow, a Sima de los Huesos in Asia, hope this turns out to be as big. Looking at the big rock in front, it does look as if some cores might have been knocked out of it. Regarding the lousy living conditions in current Vietnam, we have no idea what the climate there was like 800k years ago. It could have been cooler, dryer, or some combination depending on where it was in an Ice Age cycle. We would need more precision than a generalized age of 800K.
There's a rain forest in Malaysia ( Taman Negara) that is 130 million years old. It appears to have been fairly stable for that time and I would expect nearby Vietnam to be the same.
We may have another excellent site.