Providing JK Rowling is nice, and allows Harry to triumph over Voldemort in the seventh book, then it would be very interesting to see what happens to the Malfoys. This time around they would not be able to deny their involvement in the Voldermortian cause, but before the likely defeat of the dark lord, I am wondering if Draco would play a part helping his Death Eater father. Draco has been indoctrinated in the “pure blood mania” and harbors considerable hate towards the prominent members of the side of good (Harry and Dumbledore).
Draco has motives to help his father, but how? He attends Hogwarts and so resides under the authority of his enemies. It is likely in the next book his actions will be closely monitored so he could prove to be a liability of his father’s, as in Hogwarts there is veriserum and the great Legilimens, Dumbledore. So in the next book I can see a frustrated Draco, living with his enemies not being told anything of importance and being closely watched. With this increasingly isolated position maybe he will resort to something desperate, like for instance attacking Harry?
With increasing neglect from his father (who has always been his lifeline of gaining power and privilege) and those he admires could he perhaps soon grow bitter and switch sides to spite them? Dumbledore could be relied upon to treat him courteously and with welcome, but because of Malfoy’s background his potential defection is unlikely to happen soon. If it did happen, it would only occur in the seventh book.
As for Lucius Malfoy, perhaps he would have to leave the Malfoy mansion as he is now a wanted Death Eater. He will also be relatively trapped as there is no way out for him. Because of this, it is likely he will become more devoted to Voldemort and fight harder as his future depends on the success of Voldemort. Unfortunately, I see Lucius murdering a member of the Order of the Phoenix and perhaps that could be Tonks. She is a part of his wife’s family, but also a half-blood so is a living embarrassment to a prominent pure blood family (like the Blacks) and Narcissa could well resent Tonks’ presence in her family. In the event of Voldemort’s defeat I am not sure to whether Lucius will be killed or not (if so hopefully by a Muggleborn) so he will either wind up dead or in Azkaban (providing the dementors come back).
As for Draco, without his father he will end up poor (what a brilliant situation that would be! I’m sure Ron and the Weasleys would be very gleeful if that happened and hopefully they could get revenge face to face with Draco). So a fatherless Draco would be a very pathetic figure who would have to resort to asking Dumbledore for help if he hadn’t already. If you believe Draco would drink poison rather than resort to that then I would partly agree with you, but you would be forgetting the defining features of a Slytherin student. As Phineaus Nigellus said, Slytherins are cunning and know when to surrender themselves in order to save their own necks. This I believe is the future for Draco Malfoy, it is not a happy one but really, do we care?