Duels were a real part of the historical setting, up into the Regency and sometimes beyond. There were laws against them, and sometimes a principal who killed his opponent was executed for murder. Occasionally seconds were involved in the action, and even without they could be prosecuted. However, most cases slid by the legal system, in part because the duelers were upper class.
Here's a Wikipedia list of notable duels of the early 19th century in Britain which shows the variety of outcomes.
1803: Captain James Macnamara and Colonel Montgomery; over a dispute between their dogs fighting in Hyde Park. Both were wounded, Montgomery mortally. Macnamara was tried for manslaughter at the Old Bailey but was acquitted.
1804: Captain Best fatally wounded Thomas Pitt, 2nd Baron Camelford. He died three days later.
1804: A duel was fought on Kersal Moor, Salford in July 1804 between Mr. Jones and Mr. Shakspere Philips. Mr. Jones fired at Mr. Philips without effect and Mr. Philips then fired his pistol in the air, upon which the seconds interfered, the two man shook hands, and honour was satisfied.
1807: Sir Francis Burdett, 5th Baronet and James Pauli; both men were wounded.
1808: Major Campbell and Captain Boyd; Major Campbell was tried and executed for killing Captain Boyd.
1809: George Canning and Lord Castlereagh; Canning was slightly wounded.
1815: Daniel O'Connell and Captain John Norcot d'Esterre; d'Esterre was killed.
Of course there was a famous American one.
July 11, 1804: U.S. Vice President Aaron Burr and former U.S. Treasury Secretary Alexander Hamilton; Hamilton was killed.