Well that was the basis for my question, I'm interested in an answer from someone who understands the ins and outs of the American political system. My theory is that the seat would be inherited by her running mate which would mean if that party won then America would be run by a third string quarterback but I'd like to an answer that is definative.
No, it wouldn't automatically go to Walz.
The DNC would pick who goes on the ticket.
The issue of ballot printing is more difficult, and that would require some digging.
There are laws about when a ballot can be changed and I am pretty sure there are state AND federal ones, so untangling all that would be tricky.
Of course, no one in the United States votes for President anyway, so even if the ballot still says Kamala Harris, the electors would presumably just vote for who the DNC named.