What happened to Hyde after Jekyll dies?

Jekyll and Hyde, of necessity, die at the same time; because they share the same body, one cannot die without the other dying as well.  

When Mr. Utterson came to Dr. Jekyll's door, he hears Hyde's voice and determines to break it down in order to prevent Hyde from killing Jekyll (not realizing that they are the same person).  When he and Poole chop through the door, they see a laboratory, and "Right in the midst there lay the body of a man sorely contorted and still twitching."  It was Edward Hyde, wearing clothes that clearly belonged to Dr. Jekyll because they were too big for Hyde.  Hyde held a "crushed phial" that had contained some poison, the smell of which still hung in the air.  Hyde had killed himself rather than be arrested and hanged since he could not return to Jekyll's shape without the correct chemicals that he was never again able to procure.  There was no trace of Jekyll because he had been completely taken over by Hyde, and Utterson and Poole assume that Hyde had buried him under the floorboards (until Utterson reads Lanyon's and Jekyll's narratives and learns the truth).