I like the maxim "this too shall pass." It's easy to think of on a generational level - our fathers' generation will disappear, and so will ours. But on the level of a civilization, it becomes both stranger and sadder. Orion is a shape in the sky that humanity has always been able to see (so long as we've lived in the northern hemisphere), and one day, assuming we still grace this planet in 100,000 years, it will no longer resemble the hunter the Greeks imagined. But then, billions of years hence, all the stars will have realigned, the Milky Way will have combined with andromeda. And beyond even that, the energy will so diminish that the bonds of the atoms will release. This too shall pass.
I have found that the beauty of the temporary nature of everything (especially when considered in enormous time scales) highlights the beauty of the here and now.. and the need to enjoy it. In fact, while some say not to think of the future and stay in the present, sometimes I find that imagining far into the future is precisely what brings me back to the importance of and focus on the present.
Also, there's a feeling of pure awe I get when trying to imagine the unimaginable scale of the future (for us at least). It's a specific sensation.. I am not even sure awe is the right word to describe it.