I think that you are, as usual,correct but the power of the Democrat elites to alter the ticket, I believe, rests in the states with 50 different rules for this near unique circumstance.
I have heard that it is too late, or nearly too late for other reasons to change candidates in Nevada and Wisconsin. Do you know the truth of this or the state of play in other states?
There's nothing to prevent the DNC from deeming Biden the official candidate now that he has enough delegates pledged to justify the claim (he has since March). But once done, it can't be changed because there's no time left for that. To me it looks at the moment like the Dems have, through the inertia inherent in the system and their own indecision, painted themselves into the Biden corner. Which holds not one, but two mental deficients, because the same time constraints apply to his running mate.
There is a path open to dump both in the allotted time, (i.e. Biden leaves and the convention produces two fresh candidates) but Biden has to die, become completely disabled, or agree to resign for that to happen and it doesn't look at the moment like the clock won't run out on that one too. The default plan is, therefore, "Go With Joe" and sort it all out after he is in and Trump is safely incarcerated. However wildly unlikely that outcome is, it's the slope they're sliding down. All IMHO, of course, and it could change in the next five minutes. Ain't politics grand?