Not much can be done about the chip - this was just unfortunate. It may be the case that the particular diamond has a very thin girdle or some other details make it prone to chipping. A cutter could probably repair these with some loss of weight to the stone, IMO. How much cannot really be predicted before you actually show the stone to a cutter.
As far as I know, this is not very unusual - old diamonds come with chips...
Just my 0.2, of course.