People have gotten their eye sockets fractured or broken. Broken ribs. Broken limbs. Broken noses. Broken jaw. Dislocations, fractures, bruising. Blindness. Partial or complete paralysis.
The worst of course being death.
How likely any injury is depends upon a million factors, ranging from experience and skill to pre-existing injuries and age to safety precautions to emotion. I truly can't tell you with any honesty how likely it is that any one thing could or couldn't happen. Telling you the odds of a certain injury is like predicting what card you'll draw from a deck of playing cards.
Fact of the matter is that martial arts and fighting isn't a game to be taken lightly. Don't play around.