I'm not as ambitious to think I can restore it to a point where you won't notice it was damaged, but hopefully the result will be acceptable and you won't immediately see that several square inch of plastic was missing.
Luckily, the damage is on the underside, so you'll have to pick up the model to find it.
My best chance of repairing the damage is making a mold from a section that's intact and has the same surface detail, i.e. the other side of the saucer. I covered this liberally with liquid latex and let this dry for 2 days. (1 day is probably enough, but I didn't have time to work on it anyway)
I then carefully removed the latex from the model, but this stuff is quite resilient, so you don't need to be too carefull. The detail in the mold is better than I dared expect.