The way I understand it you want the marrow (the mushy center stuff) and vitamins/collagen etc from the bones themselves. I would not expect the bones themselves to break down but the good stuff to cook out into the broth over the 30 hours. As such you should be good to go. As for the onions and garlic etc., I see no reason not to eat them. They will in no way detract from the good stuff from the bones. You could puree it or eat them with the pieces still large depending on preference or use a slotted spoon to get them out completely.
As for reusing the bones, I am not sure how much 'good' is left in them after 30 hours. I guess you could use them again, but it would not be as optimal as fresh bones IMHO.