The End Of The Universe

Three times in Poul Anderson's works, a character or group of characters survives until the end of our universe:

by space travel with time dilation;
by time travel;
by spacetime travel.

Space travel: a Bussard ramjet.
Time travel: a conventional time machine, here called "the time projector."
Spacetime travel: via a network of T machines.

Each character or group goes somewhere different afterwards:

the space travelers survive into the next universe;
the time traveler continues forward around the circle of time back to 1973;
the spacetime travelers return to their origin point through the T machine network, having learned that there are many universes and will be one after ours.

AI's hope to survive the end of the universe by utilizing the energy of photon decay. Another group of space travelers features in a novel called After Doomsday but this Doomsday is merely the end of all life on Earth. As ever, the impression generated by Anderson's works is one of comprehensiveness.