Re: Very high.
As time goes by, the energy we use increases and so does our destruction capability.
Very soon, terrorists will be able to use a huge destructive force, or an accident will have very lethal consequences. That would be enough to send the survivors into the middle ages.
But, even if those scenarios are unikely, we might just decide not to make enough children to insure our survival as a species. We would then replace them by robots (A.I.).
Raoul