It would have been interesting if Sydney had addressed the crowd with a major speech that would have liberated the woman who was there for no reason, or he and Evremond could have plotted a huge plan to escape somehow. However, Dickens purposely avoided this and it would have never been written down. This was a novel with journalistic tendencies to report exactly how excessive the French Revolution was. The novel needed martyrs and people to pay without fairness. It is what gave the French Rev its horrifying nature. Sure a heroic ending would have been a plausible ending, but it would have undermined the purpose of the author which was to both entertain and persuade, inform and describe history in fiction and in detail.
While Darnay is a rather lackluster character, Carton certainly has potential and deserves to fulfill his life. And, there are those readers who feel Therese Defarge does deserve revenge for the heinous acts against her family, so perhaps a satisfying ending for these readers would have Darnay going to the guillotine in expiation for the "sins of the father." Having failed to rescue Darnay, Sydney Carton can rescue Lucie--thus redeeming himself--and drag Madame Defarge to the sight of Darnay's death, releasing her from her vengeful desires as she witnesses the fulfillment of them, and, thereby attaining a certain resurrection of herself, as well. But, she must pay for her hatred of all aristocrats, so she slips and has her skirt caught under a tumbril, rolling to her death under the cart of aristocrats, metaphorically demonstrating Dickens' prevalent theme of the inability of people to escape their social class.
After Carton rescues Lucie, they ride in the carriage on their escape to London. Carton reaffirms his unending love for her, and Lucie, as the true Victorian heroine, weeps in his arms both in gratitude for his love and in anguish for the loss of her husband. As they ride along, Carton ponders what the future will bring and vows to break from C. J. Stryver and now be his own man regardless of what Lucie decides.
A Tale of Two Cities would have been interesting if it had a Heroic ending. However, Charles Dickens purposely avoided this for some reason. This novel reports exactly how the French Revolution was and what gave the French Revolution its horrifying nature. An Interesting Ending could be;
"Suddenly, Charles Evermonde appeared from the crowd as Sydney Carton was about to be killed. Before claiming himself as Charles and Sydney innocent, he gave a speech trying to tell the public what was going on. The crowd understood every word he said and finally, both Charles and Sydney were saved from their deaths. Madam Defarge's death was taken as a punishment for her and everything slowly settled. Dr. Manette, Lucie, Charles and Sydney lived in peace in England. A daughter and a son were born to Lucie and Charles."