Narcissa had always been frail – not necessary physically, but it didn't come as a surprise to anyone who knew the family when she went just a bit mad after the birth of her first son. Draco wasn't a particularly vivacious baby either; in his own way, Lucius cared about both his wife and son, so he hired a young Healer, just out of university and clearly with no sense of her own value, to care for both Narcissa and Draco.
Lucius didn't pace back and forth in front of the fireplace each night in worry over his nascent family. There was too much else going on and he was not a worrying man. Obsequious and manipulative, yes, but he didn't obsess over the things that had been dealt with. By hiring the Healer to care for the sickly pair, he had done what he could. What left was to uphold the family image and continue to serve the Dark Lord, secretly coveting His power while grovelling at His feet in the hopes of some miniscule demonstration of favour.
When the Dark Lord disappeared, bested by a boy no older than Lucius's own son, triumph spread throughout the Wizarding world. But for the Dark Lord's followers, there was no triumph and there was no celebration. There was bitterness on behalf of some and sorrow on the parts of others, but the overwhelming reaction to the Dark Lord's disappearance (it wasn't death – it couldn't be death, for power could not die) from His followers was a dramatic, cut-throat scramble for pardon. Although Lucius played his own cards right, it required sacrifices. He was willing to protect his own . He gained nothing from their destruction and Lucius Malfoy was not one to play his cards for no reason.
It was not to his advantage that Bellatrix, Narcissa's sister, would not hide her devotion to the Dark Lord, but it was not unexpected that she refused to decry His teachings in front of the ridiculous Court the weak-spined Ministry created to try suspected Death Eaters. Her subsequent imprisonment in Azkaban with her husband, equally fanatic, was only to be expected after that kind of a performance. The Ministry wanted blood, wanted to seem as though the sudden turn of battle in their favour had been due to something other than a cosmic error and a distressingly fortunate infant. And so they sent His most fanatic supporters to Azkaban.
They could not have ferreted out the rest.
When Lucius awoke the morning after Bellatrix's unfortunate sentencing, he expected the atmosphere of the house to be sombre; it had been a close hit to home.
He did not expect to find Narcissa's crumpled body at the base of the Manor, clear evidence of a desperate suicide.