I think the secession would have been temporary. I would like to think there would have been negotiations and a reunification. Obviously, slavery had to go. I would like to believe that it would have been phased out, with a plan to introduce former slaves and their offspring, into freedom and productive society.
As for being vulnerable, the nation was most vulnerable, immediately after the Civil War, but Britain and France did not take advantage of the situation, as they would have likely immediately gone to war with each other. Who knows how it would have ended up, in January, 2023, if secession had been honored.
If you're kin to the Lees, then we probably are distantly related. My family has been in Louisiana, since the mid-1800s. I can't remember exactly what Ancestry.com research showed. I lost interest, after a while and stopped paying for it. Now, they won't show my research, unless I pay, so they can shove it. Lol