Apostate prophet wont have a second mum; who are the mothers of believers?

In answer to the video "Islamic Polygamy"

The prophet's wives had the title of mothers of the believers

33:6"The Prophet is closer to the Believers than their own selves, and his wives are their mothers".

That sanctified title carried several implications to those that were willing to uphold it. It is not a title of nobility but rather denotes responsibility and care towards the community. For example Zaynab one of the prophet's wives was called Barrah/pious. The prophet told her to keep her name instead of that nickname to avoid her

"giving herself the prestige of piety".

He further told his wives

"Don't hold yourself to be pious. It is God alone who knows the people of piety among you".

They had to restrain their social activities to their own houses as much as possible in order to dedicate themselves to piety and religious study, pray intensely, solidify in their memories the recitations and wisdom of the revelation so that they become means of preserving the right way 33:33-4. During their spiritual counseling activities, they had to watch for the tone of their voice when addressing the opposite sex so that they leave no ambiguity as to their intentions, or cause those with an indecent inclination to harbor inapropriate thoughts. They had to speak to males outside their close relatives from behind a curtain 33:32,53-55.

This injunction, besides it being a logical demand of modesty whenever opposite sexes interract, becomes all the more relevant if one considers the Quran's description in sura ahzab/33 of the atmosphere of rumour mongering, provocations and other verbal abuses the prophet, and the righteous members of the Muslim community at large were either already the targets of, or were potentially at risk of. There were elements within the community and outside of it that were on the look out for any opportunity to spew their malice and discredit and dishearten the Muslims. Consequently the prophet's household and the Muslims at large are given reassurance of the nobility of their status in God's eyes, and told in which manners to fend off those with evil inclinations. The best way to fend off these attacks were with ethics becoming of the nobility of their moral status as well as by adopting a modest dresscode.

The religious duties the prophet's wives had to shoulder were such, that willingly faltering in that respect would make them deserving of a more severe chastisement in the hereafter 33:30. This was meant to stress their spiritual responsibilities and the fact they had to exemplify piety, and so their moral conduct should be corresponding. As stated in 33:32, their difference with other Muslim women consisted in them maintaining and propagating moral, ethical and spiritual uprightness. On the other hand their reward will be more intense than regular people due to their higher sacrifices 33:31. This is just like Allah's addressing the prophet warning him not to falter in his righteousness and upright conduct lest he should face a double/more severe punishement than regular people 10:15,17:73-4,39:65,68:9.

There is a simple reason behind that principle, leaders in a society are the ones that establish moral standards and are emulated. Their evil does not remain their own but spreads fast and creates further evil, just as their goodness. One and the same sin may thus be requited according to different levels of severity depending on the person comitting it as well as the social repercussions of that sin.

Finally, in consequence of their designation and duties as mothers of the believers, they were not allowed to remarry after the prophet's death, contrary to regular muslim women divorcees 33:53.
The difference between the prophet's wives and others is that obviously none would ever marry and sleep with Moses', Solomon's, Abraham's or Muhammad's wives had the prophets passed away. This sanctified status is not one that was decreed because some believers would potentially desire to unite with one of them after the prophet's demise, it was addressed to the wives he already had and those in the future that would enter into a marriage with him, making clear to them the conditions of marrying him, and the consequences. To those that were already married to him, they could at anytime prior to his death, relinquish that status and be given the opportunity to leave this life of sacrifices and socio-religious responsibilities. Some of them did, prior to even consuming the marriage, unable to bear the burden of responsibility and an austere life. In 33:28-29 they are told that if their desire for this world and its adornment is preferable in their eyes than a life of sacrifices dedicated to their spiritual duties

"say to your wives: If you desire this world´s life and its adornment, then come, I will give you a provision and allow you to depart a goodly departing".

After divorce the woman would have stood excluded from the category of "mothers of believers", and she would not be forbidden to any other Muslim; for she would have chosen divorce from the prophet only for the sake of the world and its adornments of which she had been given the choice.

The prophet's wives had thus the option of requesting and getting a just and kind divorce for even such petty reasons like their desire to pursue this wordly life which God's prophet could not afford giving them in his household. No shame or stigma was put on those that did nor on those that would afterwards. Divorces with prophet occured, as already said. Also, enemies of Islam were all around Medina and within the city itself. Had there been such a potential negative consequence on a divorced woman's personal life she could have joined any opposing community just as former polytheist Meccan women joined the Medina Muslims for shelter after conversion to Islam. Furthermore, in relation to 33:28-9 referred to earlier, no muslim, and no man of any culture is required to go out of his way and ask his wife if she is happy and satisfied enough in all material aspects, especially when one is just with the wife in relation to one's financial capabilities. Further, no muslim or man in general is required to offer divorce if the wife is unhappy. On top of it, not simple divorce, with each partner going his/her way, which would be fairest in this case, but a "gracious" divorce, where the wife is free to leave as well as receive compensation if she chooses to. Yet this is what was required of the prophet, contrary to all muslims, a man supposedly seeking multiple marriages of lust.

By the time this verse was revealed, and as shown in the direct context, the Muslims had conquered the rich agricultural region of Khaybar, and the community had grown more prosperous. But while life was becoming easier for most of its members, this ease was not reflected in the household of the Prophet. As was always his habit, he only allowed himself and his family only the absolute minimum necessary for the most simple living

28:83"that future abode, We assign it to those who have no desire to exalt themselves in the earth nor to make mischief and the good end is for those who guard (against evil)".

His prestigious status as a prophet and ruler never came in the way of that humble principle of living. Not only was he not ever one to ask for any kind of reward from his addressees 6:90,25:56-7,12:104etc but every occasion where he could make use of his status and deep knowledge for material benefit, he would do it for the sake of the needy

58:12"when you consult the Messenger, then offer something in charity before your consultation; that is better for you and purer". 

The prophet's wives on the other hand naturally were longing for a share in the comparative luxuries which other Muslim women could now enjoy. His wives often stated that they had little on their shelves besides bread flour and dates. But it is reported that all of them rejected a possible seperation with the prophet and resumed their spiritual duties as "mothers of the believers", and were promised a great reward in the Hereafter for having denied themselves the ordinary comforts of life by remaining in the Prophet's house 33:31. Their voluntary worldy sacrifices can only be understood from a spiritual perspective.  Umm Habiba, one of the prophet's wives had such awareness for that spiritual favor despite the sacrifices that she even proposed the hand of her own sister to the prophet 

“Are you interested in my sister, Apostle of Allaah?” He said “What should I do?” She said “You marry her” He said “Your sister?” She said “Yes”. He said “Do you like that?” she said “I am not alone with you of those who share me in this good, my sister is most to my liking. He said “She is not lawful for me.”