There are exogenous threats to human civilization, such as meteorites plunging from space and creating global extinctions, possibly including us, and as Stephen Hawkings points out, the only way of avoiding them for certain is to colonize other planets. That needn't involve the bodily transportation of humans, once human genomes and brains can be electronically represented, as is described in Chapter Thirteen, and may therefore be possible in the not very distant future.
Apart from meteorites and clouds of poisonous space gas, there are terrestrial events that could be threatening, such as massive volcanic activity, or a devastating epidemic which killed such a high proportion of humans that progress would go into reverse. Neither has happened in the last few million years, and the timescale of our escape from this planet is presumably to be measured in hundreds of years; so the chance of our being stopped is pretty small.
Of course, we may be being watched by little green men, who are going to stop our escape!
There is not much that can be done about such threats, so no more words will be devoted to them here.