Love and loss could be a theme. The last contact might signify the end of a relationship, and the story could explore the emotions that come with that. For example, regret, longing, or acceptance.
Isolation could also be a theme. Maybe the last contact shows how the characters are becoming or already are isolated from others. It could be physical isolation, like being alone on an island, or emotional isolation due to some event or personal choice.
I haven't read the specific 'last contact short story', but generally, when analyzing a short story, we can start from the characters. For example, we can look at their personalities, motives, and how they develop throughout the story. Also, the plot is crucial. It might have a beginning that sets the scene, a middle with rising action and conflicts, and an ending that resolves things in some way, whether it's a happy ending or a thought - provoking one.
Another theme might be change. If it's the last day of an era, it shows how things are about to transform. For example, a society that has been stagnant for a long time may be on the verge of a big shift after this last day, and the story could explore the resistance or acceptance of that change.
Another theme could be truth. Maybe the last answer is the truth that has been hidden throughout the story. It could be a moment of realization for the characters or the readers. For example, in a mystery short story, the last answer might be the true identity of a mysterious figure. Also, redemption could be a theme. The last answer might be a way for a character to redeem themselves, to make up for past mistakes or wrongdoings. It could be a powerful moment of self - discovery and growth for that character.
A theme of regret could also be present. Maybe she has some unfulfilled dreams or things she didn't say in time, and her last wishes are an attempt to make up for that. Also, the theme of mortality is obvious. The fact that she is dying and making these last wishes makes the readers confront the idea of death and the finality of life. For example, if she wishes to see a sunset one last time, it shows her awareness of the limited time she has left.
Loyalty is a possible theme. The dog may stay with the old man through thick and thin.
One possible theme could be love and lust. Since it involves a mistress, there's likely to be an exploration of the passionate and often complex relationship between two people who are not in a traditional marriage or committed relationship.
One possible theme could be change. Since it's the 'last' Christmas, there might be a change in the characters' lives like leaving Vermont.
Love might be a theme. Maybe there's a love story that reaches a turning point on the last day of June. It could be a day of rekindling an old love or saying goodbye to a loved one.
One possible theme could be the idea of seizing the moment. Since it's just a weekend, the characters might realize that time is short and they need to make the most of their time together, which leads to the development of love.
One possible theme could be heroism. There were many heroes on 9/11, from the firefighters who rushed into the burning buildings to the passengers on Flight 93 who fought back against the hijackers.