Things that are meaningful can be lost or destroyed but it doesn't follow that therefore they were meaningless while they existed.
The point of many of the things we do involves attaining certain goals and what happens after doesn't change the fact that certain goals have been attained.
The value of some things resides in the fact that they actually come to an end (too much of a good thing).
First thing: your question is not a possibility, it shouldn’t start with “if”, because the disappearance of everything in the future is a scientific fact. The sun is just a star and, like all stars, it has its process, from its birth, with several stages, until its end, its death. So, you can just delete the initial “If” from your question.
Second thing, I disagree with Pfeiffer’s faith in the meaningfulness of things just because they existed, they happened. We know that even time is subject to distortions, alterations; we as humans exist inside this thing that we call “time” and we have no idea about how something can keep an importance independently from time.
Your question, actually, is very old, people have reflected on it without needing our advanced astronomy knowledge. Philosophers, of course, still reflect on it, you have just to choose which line of thought you prefer.
At this point I think a good question is: what are good ways of dealing with your question?
I think that science is useless about this, because its field is very limited: it is limited to what can be scientifically proven, while the concept of “meaning” is much wider. Some people have even thought that what we consider “meaning”, “meaningfulness”, doesn’t help about the value of things, because it is very dependent on our mentalities, that are conditioned by our historical conditions. So, from a certain critical point of view, meaningfulness is actually a mental concept that reduces the value of things, because it reduces it to what our little brain is able to understand.
In my opinion, after considering all of these things, the best way is to deepen our ability to manage criticism, try to deepen more and more our awareness about our limits, our condition as human beings, our weakness. From this point of view we might even notice that your question can be even considered an evil question, because it is looking, although out of your intention, for power, control, supremacy, that is a kind of human mentality that has ruined the world and has filled it with violence. There are philosophies that, to avoid this, cultivate perspectives of weakness, humanity, humbleness. They try to go against the common current in nature, based on power and competition.
Of course, one may not have the same ideas. But this is valuable in terms of diversity. Why did I include if, because scientific facts can also change. You state that the question I asked you seems evil etc., but questioning liberates us. This includes questioning the ideas we question. Thank you for sharing your point of view and ideas, Researcher Angelo Cannata
I think it is better to clarify: I don’t think at all that your question is evil. I like to explore philosophy and, like a philosopher, I like to explore how a lot of different perspectives work, even weird perspectives, I like to play with them, because they can show how our reasoning works. I was just exploring a perspective.
In my view we make of the world picture our own reasons for life. I have never thought myself intelligent enough to grasp an absolute truth without a mighty leap of faith. However, from my experience there are many things one can believe in that are not so profound as the end of history yet still require some level of faith in order to form a belief. As many philosophers have reiterated, not every question has a final complete answer, often it's just a matter of finding something that works for now.
I want to create a thought free from blurred thoughts. I agree with the idea that people interpret things from their own point of view and/or perspective. ("In my view we make of the world picture our own reasons for life.")
Thank you for sharing your thoughts.@Peter Thomas Byrne Gregory