Yeh, they did.
They were extremely smart people.
And they considered the possibility of that happening.
They calculated the probability of it happening, considered their known-unknowns and unknown-unknowns in their calculations, and concluded the possibility (including their error margin) was so incredibly low that it wouldn’t happen.
And they were right.

A scary prospect, to be sure.
But ultimately, that’s what experts do.
Anyone can build a bridge that will stay up, but it takes an engineer to build a bridge that only barely stays up.