A convention outcome would be horrible for the party

I cant speak for every state but will use Illinois as an example. We actually have two elections the popular vote and the delegate election. Only Biden filed delagates so they will be "Biden" delegates. These folks were selected by the campaign by Congrssional District. Some are elected officials while others are just active party members.

As you would expect the delegates vary in terms of their politics from moderate to progressive but if Biden withdraws I dont think they would be required to support any particular candidate. The "party" would have no ability of the party to enforce who they want to be the nominee other than to appeal to people's better judgment. Needless to say given the breadth of views within the party arriving at a consensus candidate would not be easy and would creat a lot of uncertainty around the election.