Question is simple Buddhist believe in an endless circle till you have reached a certain enlightenment and I know quite a few people on this board believe in Reincarnation in some form with us in some cases being willing and in others unwilling participants in reincarnation. So the question arises what happens when the soon expands to engulf the earth destroying all living creatures on earth. What happens to reincarnation then? And don't tell me that by then humans will of started settling on planets further away from the sun because our nearest galaxy is also due to collide with ours.
People are already settling into other planets, and always have been in small numbers. If - by some chance - the Sun expanded to the point of consuming the Earth, it would be a very gradual process. The results would vary greatly from person to person.
Secondly, when galaxies collide, life is only marginally affected, because the stars are so distant from each other that there's a very slim chance of two stars colliding. Some say our own galaxy is a hybrid of two galaxies that collided not too long ago.
If a huge, sudden catastrophe destroyed the planet, the remaining spirits would incarnate on another planet, or remain in space, or just stay on the destroyed planet
The Sun's expansion and then destruction of earth is not for another 5 billion years or so, as the sun is middle-aged now.
When there are no more life/experience offerings on earth souls will go elsewhere for experiences, just as we have been elsewhere before coming to here.
No biggie if the Sun goes Boom.