Terminus was attacked, numerous times but not 'destroyed'
It's foggy since it's been so many years but the largest threat I remember was the Mule. An aberation that defies psychohistory, which Selfon has, of course, predicted and planned for.
Also, there were no AI Seldon. Seldon just leaves recording of himself in the vault.
The story never really focus on the infividual 'chosen one' it's more about the world and mechanism of civilization. (Well, apart from Daneel)
I might need to re read it again soon.