If yes, then they should be treated with the reverence due the holy Body and Blood of Jesus. They must not be mixed with unconsecrated elements (i.e. put back with other hosts or poured back into the bottle of wine). They may either be consumed (eaten) or reserved (stored apart from unconsecrated elements).
If no, then they may be treated as normal bread and wine.
It is the Word of Jesus alone, not my faith, nor my lips, nor my receiving the elements, that effects the presence of Christ's true Body and Blood. "The word of the Lord endures forever" (1 Peter 1:25). What Jesus says goes. His powerful, creating Word brings about the real presence of His Flesh and Blood. Why would we assume that our action (our singing the Nunc Dimittis or otherwise "ending" the action of the sacrament) would be powerful enough to terminate Jesus' presence?
So, yes, what has been consecrated is and remains the Body and Blood of Jesus in, with, and under bread and wine until Jesus' command is carried out completely. That is, until everything consecrated has been eaten and drunk ("Take, eat;" and "Take, drink.").
Therefore, it us unLutheran and indefensible to mix consecrated bread and wine with unconsecrated.
When Luther heard about the scandal that had arisen in Eisleben over how the consecrated bread and wine should be treated after the Supper, he wrote this to Lutheran pastor Simon Wolferinus:
We do not have it from you, but you from us that the sacraments are actions, not stationary objects. But what is this singular temerity of yours that you do not refrain from so evil an appearance—which you ought to know is scandalous—namely, that you mix what remains of the [consecrated] wine or bread with unconsecrated [Latin: prior] bread and wine? On the basis of what example are you doing this? Do you not clearly see how you will arouse dangerous questions, if, ‘‘convinced in your own mind’’ [cf. Rom. 14:5], you contend thatthe Sacrament ceases when the action ceases? Perhaps you want to be called Zwinglian? I believe that you are afflicted with the insanity of Zwingli, you who so pridefully and contemptibly incite [matters] with your singular and glorious wisdom.Was there no other way to avoid suspicion being sown among the simple and our adversaries that you are a despiser of the sacrament, than by your giving offense with the evil appearance of mixing and confounding theremains of the sacrament with [unconsecrated] wine? Why do you not imitate other churches?Why do you want to be held to be the only, newand dangerous author [of this practice]? I write these things in this manner with deep sorrow, so that you may know that you have offended me and profoundly saddened my spirit.
The dispute was not so easily settled by Luther's correspondence. In 1543, he wrote a second letter to Wolferinus, saying
Therefore, we shall define the time or the sacramental : action in this way: that it starts with the beginning of the Our Fat her and lasts until all have communicated, have emptied the chalice, have consumed the Hosts, until the people have been dismissed and [the priest] has left the altar. In this way we shall be safe and free from the scruples and scandals of such endless questions. Dr. Philip defines the sacramental action in relation to what is outside it, that is, against reservation of and processions with the sacrament. He does not split it up within [the action] itself, nor does he define it in a way that it contradicts itself. Therefore see to it that if anything is left over of the sacrament, either some communicants or the priest himself and his assistant receive it, so that it is not only a curate or someone else who drinks what is left over in the chalice, but that he gives it to the others who were also participants in the body [of Christ], so that you do not appear to divide the sacrament by a bad example or to treat the sacramental action irreverently. This is my opinion and I know that it is also Philip's opinion too.
Martin Chemnitz, one of the authors of the Formula of Concord, in refuting the Roman Catholic Council of Trent argues similarly: