I read your 2013 post on hornet nest (very informative). Do empty nests eventually fall off the tree or remain?
Howard County Maryland
The old nests eventually weather away, and birds may peck at them too, exploring for overwintering insects taking shelter inside, which will speed-up their disintegration. Wind in storms and ice/snow loads can also snap the twigs that the nests are attached to, and once on the ground, various decomposing organisms degrade it further.