This is going to sound ridiculous, but thinking about time as a 4th dimension helped me. The past never disappears from our universe, it's just the previous page of the book we're reading, and always there just a short distance away along the axis.
This helped me reframe the loss from "they're gone forever" to "they're alive, in the past".
It's now an inaccessible location to you, but the past exists in no less of a real way than the present moment.
And while that's not the page we're on anymore, that ink never fades. You shared those pages with them.
And if it occurs to you to think this way before they're gone, then I hope it also encourages you to fill those pages with the happiest times together that you still can.
The most important thing I learned on Tralfamadore was that when a person dies he only appears to die. He is still very much alive in the past, so it is very silly for people to cry at his funeral. All moments, past, present and future, always have existed, always will exist. The Tralfamadorians can look at all the different moments just that way we can look at a stretch of the Rocky Mountains, for instance. They can see how permanent all the moments are, and they can look at any moment that interests them. It is just an illusion we have here on Earth that one moment follows another one, like beads on a string, and that once a moment is gone it is gone forever.
This helped me reframe the loss from "they're gone forever" to "they're alive, in the past".
It's now an inaccessible location to you, but the past exists in no less of a real way than the present moment.
And while that's not the page we're on anymore, that ink never fades. You shared those pages with them.
And if it occurs to you to think this way before they're gone, then I hope it also encourages you to fill those pages with the happiest times together that you still can.