What would have happened if Mathilde Loisel had not lost the necklace?

Mathilde Loisel would not have had many opportunities to play Cinderella at the ball. She was not the promiscuous type, like the wife of Monsieur Lantin in Maupassant's story titled "The Jewels," or "The False Gems." Mathilde is obviously a dreamer. She would go back to her normal humdrum existence and continue to fantasize about 

...silent antechambers, heavy with Oriental tapestries, lit by torches in lofty bronze sockets, with two tall footmen in knee-breeches sleeping...

Mathilde Loisel would not have had many opportunities to play Cinderella at the ball. She was not the promiscuous type, like the wife of Monsieur Lantin in Maupassant's story titled "The Jewels," or "The False Gems." Mathilde is obviously a dreamer. She would go back to her normal humdrum existence and continue to fantasize about 

...silent antechambers, heavy with Oriental tapestries, lit by torches in lofty bronze sockets, with two tall footmen in knee-breeches sleeping in large arm-chairs, overcome by the heavy warmth of the stove. She imagined vast saloons hung with antique silks, exquisite pieces of furniture supporting priceless ornaments, and small, charming, perfumed rooms, created just for little parties of intimate friends, men who were famous and sought after, whose homage roused every other woman's envious longings.

Feminine beauty and charm has evolved for the purpose of reproduction. Women have to attract men in order to have babies, and they reproduce successfully if they can hold men while their offspring are growing to adulthood. Mathilde would undoubtedly have gotten pregnant. That's generally what happens when women get married. Then her interests would probably have centered on her children, and the "silent antechambers, heavy with Oriental tapestries" and the rest of it would have vanished like dreams. Her misfortune was that she had not been able to marry a man who would have been able to provide more of the luxuries she had read about in novels. But marriage was a more binding commitment in Maupassant's day. Mathilde was stuck with the nice little man she married. She wouldn't have started having "affairs" with other men, and she wouldn't have thought of getting a divorce. Her fate was practically settled when 

...she let herself be married off to a little clerk in the Ministry of Education.

There must be many women who regret being married to the men they end up with. They must dream about how their lives would have been more comfortable and more interesting if only they had married this or that other man. The invitation to the Minister's ball in "The Necklace" only provides a brief opportunity for Mathilde Loisel to revel in the attention of men who are superior to her husband--

...men who were famous and sought after, whose homage roused every other woman's envious longings.

The ball is only like a continuation of the dreams she has when she is alone at home. It is not the ball that makes the big difference in the story, but the loss of the borrowed necklace. If she hadn't lost it, her life would have been the same as before. She would have become a mother and a lower-middle-class housewife. She might have learned to accept her lot in life. She might have even become happy.