We normally tell stories in past tense. In general, we don't care if a statement might still be true today. We still give it in past tense because we are relating something that happened in the past. Most of the time, discussing whether the event is still true or is true again would be irrelevant to the story and distracting.
Like suppose I am telling the reader about events that happened ten years ago. I write, "Sally was visiting Chicago." The fact that I use past tense just means that she was visiting Chicago at that time. She may still be in Chicago, she may not. She may have left and gone back.
In many cases, it would be impossible to say whether a statement that was true at the time of the story is still true today. I have no way of knowing when the reader will read the book, or what the circumstances will be at that time. Someone may read this book tomorrow, and another may read it 100 years from now when Sally is long dead.
It's routine, for example, to write descriptions in past tense. "George entered the room. He was a tall, black man with wavy hair. He wore a red shirt and blue pants." If George is still alive, presumably he is still tall and still black. He may or may not still have wavy hair. He may have decided to get a different hair style, or he may have gone bald. And of course there's no assurance that he is wearing the same color clothes.
You know this. And so does the reader. If every time you described a character you said, "He was wearing a red shirt that day, but when I saw him today, as I write this story, he was wearing a green shirt, and of course I have no way of knowing what color shirt he'll be wearing at the time that you are reading this", well, that would just be tedious and pointless.
It could also give away information that you don't want to reveal yet. If you make a point of telling the reader what George looks like today, that tells the reader that he is still alive and perhaps other information about him. If later you try to create suspense about whether George will survive his adventure, well it would blow it if you told the reader that he is still alive at the time you wrote the story. And of course, if you tell us that every character is still alive and then pointedly don't mention this about George, that would be a clue to the observant reader that George is not still alive.
I can only think of 2 times when we shift into present tense:
When discussing some eternal truth, or at least, some fact that we would presume will be true indefinitely. Like some fact of science. If I was telling a story in which, I don't know, the hero performs electrolysis on water to produce hydrogen gas, I might say, "And then he poured water into his electrolysis apparatus to produce hydrogen gas. Water is, of course, made up of hydrogen and oxygen." i.e. "is", not "was", because presumably it always was and always will be. Not quite an eternal truth but a long-lived one, I might break into present tense to say, "Italy is a peninsula jutting into the Mediterranean Sea". Etc.
If you are making a point that something has or has not changed since the time of the story. Like, "The explorers constructed a monument to mark the site of their discovery, and it still stands there to this day." Or, "In those days Ruritania was a monarchy. It did not become a republic until centuries later."
There may be other cases, but they're all relatively rare.