Rat, opossum, snake, raccoon, skunk... there are a lot of possibilities. The lack of disturbance doesn't really mean much because many small predators are very nimble and don't knock things over. If there was wet ground around the nest so you could see prints you could probably identify the source, but given that it was hard substrate and the eggs and hatchling are gone you're only left with "something big enough to either eat everything all at once or carry the rest off". Leaving the nest is a good idea -- if the parents survived they may try to renest there.