Can quartz or granite be repaired if it chips?

Both can, and both repairs are visible if you look for them. A chip on an edge or around a sink cutout is filled with a colour-matched resin and polished flush; on a busy granite pattern it disappears at normal viewing distance, on a plain quartz you will know where it is. A crack across a span is different and usually means replacing that piece. Most chips happen at the sink cutout during the first year, which is why the fabricator should be the one to come back and fix it.