Regardless of what the threat is, in many
cases the ability to weather the storm at
cryogenic temperatures would
allow time for the threat to blow over so that those at greatest risk
can survive while those (or those mechanisms) in a better position to
combat the threat at normal body temperature do so.
Uploading
A personality could be
uploaded or migrated to a computer as well as being
broadcast to the universe so a future ET could
reinstantiate them in case an existential risk occurs. Instead of an
ET, if one is willing to entertain either faster-than-light travel or
non-Euclidean-space travel (e.g. wormholes), it may even be possible
that our far-future descendants pick up our broadcasts and reconstruct
us.
Time Travel
By travelling at very high speeds, time would slow down for the
traveller
per Einsteinian Relativity.
