If the Democrats do push Biden out, I predict there will be no consensus on a replacement candidate, leading to infighting and, ultimately, a realization that the Democrats have a stable full of flawed candidates that cannot gather national support, particularly in a short time window.
if you lean on everyone hard enough and successfully enough, you can get people all-in for Harris as Biden's heir at a convention. (do I bet everything I've got on that as a possibility? I do not.)
to be clear I think Harris is probably a weaker candidate than Biden, especially in the Midwest states, and I haven’t seen anything yet that persuades me otherwise
I think there are voters who will vote for Harris but not Biden. Do I bet there are more of them than there are voters who will vote Biden but not Harris? I do not. ("Will you keep using all these gambling metaphors?" "You can put money on it.")