Maybe! But as long as Hellary is breathing I think she will be maneuvering to run for Prez.
My view only... Hillary is damaged goods within her party. A 2-time loser and worse... she’s old and demonstrably sick. Biden is the same, but it’s been a while since he last ran (for president) and the Millenials have no recollection of his previous electoral debacles. He may up being a ‘place-holder’ as you say, but that will depend on how much early strength he shows. Right now he’s looking like he’s checking all the boxes. His problems remains... wrong color, wrong gender and wrong sexual preference. But if he’s still standing at the convention, he could be everybodys’ second pick (which is right where you want to be at a brokered convention).