Interesting read there my friend & a great piece of history you have there with the pistol & letters..
Back to the question.
If loaded properly "IE chambers deffinitly dry, powder then wad & or Ball over top then maybe grease over the ball & a good seated cap" & if the weapon is not subject to the elements it should last for several years & still be reliable enough to fire off the loaded chambers.
I've had my 1851 Navy loaded for more than 1-2 years once & only had one chamber fail to fire on the first attempt but after the second cap it too fired & kept the acuracy as though it had been loaded that morning.
I occasionally will keep either my 1858 "8 inch barreled or 5.5 inch barreled" or my 1860 loaded for going out back & sometimes they'll be loaded for a few months before I get a chance to shoot them off, when I do that though I usually will have a bit of finger nail polish around the cap & nipple to keep from moisture from getting into that area of the cylinder "do that mostly for when I do have one loaded in this maner & I'm caught out back & it rains a bit." "Before any one rings in, I some times carry one of my toys instead of my regular deffence pieces because I can shoot them just as well as I can my .45ACP or 9mm, just sometimes I feel like doing so & because I can."