> Either the Brexit example is a simple mistake or you're confused
Or it is exactly what it was offered for, an example of an actual withdrawal that, once triggered, takes time, which is why the “(like Brexit)” parenthetical was placed precisely where it was but not (for instance) after the reference to th negotiate-then-cancel strategy, which wouldn't mechanically work with Brexit, as you note, and had never been suggested to be the strategy of Brexit (though trying to effect a cancellation in the face of failed exit negotiation send to be emerging as an idea in some significant corners of British politics, but that's a different thing.)
Your essay was well-crafted, but entirely misplaced.
Brexit: the "exit" part takes place over two years, but is irreversible once the process begins. Re-joining the EU requires unanimous approval from all then-current members of the EU.
Postal treaty: the exit takes place over one year, and is reversible at any point during the year. Re-joining the treaty is a simple matter of re-ratifying it through your legislature (i.e., the US Congress) because all UN members are automatically entitled to join the treaty and are not subject to any sort of membership vote. (Non-UN members are subject to a vote by the membership.)
Or it is exactly what it was offered for, an example of an actual withdrawal that, once triggered, takes time, which is why the “(like Brexit)” parenthetical was placed precisely where it was but not (for instance) after the reference to th negotiate-then-cancel strategy, which wouldn't mechanically work with Brexit, as you note, and had never been suggested to be the strategy of Brexit (though trying to effect a cancellation in the face of failed exit negotiation send to be emerging as an idea in some significant corners of British politics, but that's a different thing.)
Your essay was well-crafted, but entirely misplaced.