Thank you for articulating some of the problems of a last minute replacement for Biden. Although compliant Dem state legislatures would probably rush to change whatever laws are needed to overcome issues like that, a la Frank Lautenberg’s last second senate “campaign” in New Jersey years ago.
The only way it works is if they replace Biden with Kamala Harris. Then the ticket is intact.
So, I think all this talk of replacement is just talk.
In 2020, the same brain-trust said Biden would resign weeks after he won, weeks after inauguration, weeks after X.
It never happened and as long as the fascists see a path to propping up Biden, they will stretch this out.