“we need to delay the election”
That has never been done before. Not even with CW 1. A cancelled (or “delayed”) election on account of an individual’s health would mean that the US has devolved officially into a despotic oligarchy. This would be a tipping point and would give license for anyone to flout the law. IOW civil war.
There can be no legal cancellation. If the Dems don’t have a candidate to support that is too bad. Hillary and Trump aren’t the only ones on the ballot.