Can it be that easy that all the key Democrats will just accept Kamala as Biden's successor?I think Kamala would be their best chance at this point. If they don't go with her it will cause further mistrust (if that's possible at this point) in that she was chosen to be the VP, and in the event something bad happened to Biden she would assume the role of POTUS. So if she is not chosen now, that entire decision will be scrutinized by both parties.
Will some prominent Democrat(s) step in and challenge Kamala?
After all, if there was a primary contest there would have been a serious challenge to Kamala. We know VPs often do not come up on top when seeking the Presidency.