I think that they did know and anticipate it, they wrote about it and told us what it would take to keep it. The enemies of freedom have been chipping away at it since then, lying about and revising history to match their narrative to destroy the USA and the freedoms we have in the name of equality for all except themselves, some being more equal than others.
I believe that is the reason they created and defined the second amendment, so that honest and free persons can maintain their freedoms from the evil that seeks to consume us all.