Oh there is no doubt. It would be tough to do if they just have Harris run because she is on the ticket already and the successor to him but anyone else and the GOP will sue and have an arguable point to keep them off the ballot. There isn't enough time to get enough signatures to make it work. Not to mention voter rights groups will sue the DNC to block the change as well... And then lets say all of the new candidate survives all of that he/she is going to be so far behind in fundraising they might as well just quit anyways. The $240 million the Biden Camp has right now (which includes ridiculous fundraising since the debate) does not transfer. Some might if it is earmarked for the Party not the candidate, but anything raised by Joe or in Joe's name goes back to the donors.
If all of these Old White People are so scared, why didn't they back Dean Phillips when he ran in opposition? A solid protest vote in his favor and you have a completely different scenario right now.
And I will continue to say it is "Old White Men" who mostly care about all this because it is. The Congressional Black Caucus, The Hispanic Caucus, The Progressive Caucus and most of the big money donors (despite what cnbc is putting out there) have all backed Biden.