The Sun will last millions of years. Have humans not been able to invent spaceships or any other way to survive in millions of years? At that time we should be as technologically advanced as kryptonians. And Superman didn't use kryptonian technology to help? In millions of years Superman hasn't met other aliens in other planets that could help human kind? Green Lantern Corps? New Gods? Anybody? Are we humans so ******ed that we'll die in this planet because we couldn't find a way to leave it in millions of years, even knowing that there is life in other planets, knowing a super-powerful alien with advanced technology who could help us and surely knows other planets with life, or just inventing something by ourselves? Because colonizing other planets is being studied today in "real life", and in 100 years we passed from riding horses to travel to use rockets to go to the Moon, technology has hugely advanced in around 1 century, so I think that after millions of years we should get something to survive to a dying Sun...(In millions of years we could have an artificial Sun or something similar, we could even not need a Sun at all, who knows).
P.S.-Sorry if my english is not good enough.