Technically they put someone else in atheir convention which is a long way off.
The dimrat bylaws say that after a nominating convention, if the candidate becomes disabled or disqualified, then the DNC alone appoints the replacement. In short, anyone they damn well want.
That convention is going to be very interesting, for a lot of reasons-
Will Biden be allowed to participate?
Who else will be seeking the nomination?
Will this be “Chicago 1968” all over again?
Are there other “monkey wrenches” to be thrown in to the process?