[antepodius]

Depends what the possible futures you're envisioning are. If some crazy hive-mind/brain-upload/matrioshka brain/turn the universe into computronium future happens, what you do now could influence part of the course of that.

I don't get the 'either we destroy ourselves, or the sun explodes'. If we don't destroy ourselves now, there's no way humans just stick around in the solar system till the sun explodes- at one point, some civilisation will invent brain uploading or general AI or something, and then they'll go and eat the Galaxy. It's either that or total extinction. I can't envision a very likely future where humans survive for Billions of years as-is.

[cataphract]

Either way, the universe will undergo heat death. So on very long timescales nothing will be left. Also, we don't have "billions" of years on the planet, more like 1 billion tops. Life on Earth is on its final stretch.