There is a 4 foot long crack in the center of my counter. Apparently, the installer did not brace underneath it, and when I dropped something heavy on it, it cracked from the end of the counter almost to the sink. Is there any way to repair it?

Yes, Corion is very easy to repair. But first you should call the installers and complain. Maybe they will fix it for free. Either way it needs to be professionally done since you cannot normally buy the proper cement for the repair.