 Why did the main character no longer keep the ruby necklace?
"It's for you; so long as you wear it, I'll come back, even from the dead, if need be. She took off the locket she wore about her neck and held it up to the shimmering light, letting it spin at the end of its chain. Those who had remained alive had found a resting place on the crown of some distant mountain. Even their governments had vanished, leaving a silent nothingness. The armies that remained were without leaders, without sources of supplies, save what they could forage and beg from an unfriendly people. Their families had long since died, their bodies turned to dust, their spirits fled on the winds to a new world.
 The love that was symbolized by the necklace is now gone.
 He would rather the monster have the necklace.  He wanted the necklace to remain with the house where his love was.  He figured his wife might come back for the necklace and know that he had returned from war.  The love that was symbolized by the necklace is now gone.