2x when I lived in NC 10 yrs ago there was a 24/7 drop off at a meat locker at the ag center you filled out a form to tag the carcass & they sent you a report & invoice for like $25 in just a few days.. Are you within driving distance of your state diagnostic center? If you are and can do it, get a necropsy done so you know what you were trying to deal with. Ours charges minimal fees for diagnostic necropsies.
Also, yes I have found that dairy goats can be tricky that way, they can be so stoic you don't even see any problem just fine then dead or fine then acting a little off then a few hrs later while you are still trying to figure out if you imagined them acting odd suddenly dead, it is like there is no middle ground on goats it is either super robust healthy or zero goat : (