You are right. He married Catherine Dolgorukova and died the next day. They, supposedly, pushed her into bed with him the night of the wedding. Of course, there were no children and thus ended the direct maile line of the Romanovs. He was suceeded by his cousin Anna Ivanovna, who was the daughter of Ivan V and the niece of Peter I.
It is rather pathetic, isn't it?
Intrigued by Prince of Poland's query, I began some research to see if there was any rumor about a child from the short-lived, unconsumated marriage, and found nothing.
So, what happened to the Czarina Catherine? She was married to the Czar, afterall--even though he died--but that wasn't her fault.
"We make a living by what we do; we make a life by what we give" Winston Churchill
The marriage did not take place, this is speculation. Her family tried to usurp the throne, so they were beheaded and she was sent to Siberia by the rightful Empress Anna. Then returned back by another usurper - Empress Elizabeth.
It was rumored that he and Elizabeth Petrovna, who would have been his half aunt ( his father's half sister) were actually lovers- they were close. He led a wild life for someone who died only age 14-15.