Some Other Risks
Which are reasons for colonizing space starting but not ending with Mars.
Inevitable:
Solar expansion
Likely (in the sense of known possibility, not probability > 50%):
biowarefare agent generated plague
nuclear war
extinction level impact
civilization destroying impact
Possible:
nearbye Gamma ray burst (I think these events decrease in probability with time)
another world war with greater destruction collapsing civilization
Unlikely:
Hostile aliens.
Grondine placed in position of authority in world affairs. ;-)
Regards,
Mark