You might look up "Balut".
Whether the egg goes bad to where it is not safe to eat depends on whether bacteria is present. If bacteria is present, the egg goes bad, whether it is fertitlized or not and whether it has started to develop or not. If bacteria is present, the nutrients inside the egg are really good for that bacteria feeding and multiplying, and incubation temperature is just about perfect for rapid growth. Eggs can go for a long time without going bad if bacteria is not present. If bacteria is present, they go bad pretty fast, especially at incubation temperatures.
So it is quite possible that the egg is safe to eat, especially if cooked properly. But your question was whether it was edible, not safe. I personally could not get past the yuk factor and eat it, so while it may be safe, to me it is not edible.