What would happen if a person tried to commit suicide by stabing carotid artery but missed?

Serious injury : You would experience serious injury, may not die, but will have to deal with serious physical injury and making a suicide attempt.

Depends...: There are many important structures in that area - your wind pipe , vocal cords, nerves, thyroid gland. Blood vessels, neck muscles, esophagus, neck vertebrae.If you know someone who is considering this, help him/her get urgent care. You may need to go to the closest er or find a psychiatrist that can evaluate the person asap. We must take every threat to harm one's self seriously. Take care.