Ok, not the best thing, but not the worst.
The good news is the chip is circular, so ypu won't see any additional diffraction spikes ilike if the chip had a straight edge. Another good thing is though it looks HUGE, the % lo st isn't all that significant. Your bird can still fly!
If you like, you can paint the chip matt black to stop any reflections that may come off the substrate glass, being carefull to keep the edge round. Or cut a similar sized scallop out of black self adhesive felt to put over the chip to do the same jib as paint - could be easier and safer than paint. I've got plenty of the stuff and wpuld be happy to post you out a piece rather than you buying a whole lot for just a small piece.
Alex.