I learned about these pistols at a very young age(let's skip the tv shows....reference one of the best books ever written circa 1880's Treasure Island when Israel Hands meets his demise - trivia: this fictional character was the actual name of Blackbeard's #1 man in real life who of course was also killed by Blackbeard...)
In one of James Fenimore Cooper's Natty Bumpo books the hero and companion are ransacking a trader's possessions , the trader having been a pirate in his younger days.
They find a set of fine dueling pistols and try them out. The barrel bursts on one pistol, they then put both pistols back where they found them.
In the sixties I found a article in American Rifleman with photo spread of George Washington's pistols.
One was a set of very nice dueling pistols that matched the description in the Cooper novel. These pistols had been stolen around the time the Cooper novel was set and later returned under mysterious circumstances with one pistol having its barrel blown out in exactly the same manner as that described in the novel.
Normally a muzzle loader would only be left loaded for a few days at most, then either fired and cleaned then reloaded, or the ball drawn using a worm the charge inspected and either replaced or reloaded.
Damp powder was simply dried out and reused.