More so than pissing off die hard Trump supporters or generating a sympathy bump, I think the logistics of the election being a month away and Donald Trump's name being on almost all the ballots probably causes enough confusion to tank Republican turnout, or cause some rather weird splits or people writing in Pence's name instead.
If I'm being one hundred percent honest, I think this would happen, and biden wins by default. All early mail in votes for trump have to immediately be discarded, and thousands of people who still vote "trump pence" probably do so thinking the counters would differentiate him being dead but they won't. The only votes pence gets are ones where they could change the ballot on time or he gets write ins, probably only netting him states where biden LITERALLY already a 0 percent chance of winning.
Morgan Kingsley -
March 28 2023
To be fair the ballots wouldn't be discarded but the logistics of how all this works isn't simple.
The Republican National Committee has to convene a meeting no earlier than 10 days (per their own bylaws) after Trump's death and only then, officially, can they declare Pence the nominee and whoever he wants as his VP. But given it's October and there's no way you're changing any ballots, you're still going have to ask people to vote for Trump for President.
Most states don't have faithless elector laws, and most that do have exceptions including for the untimely death of a nominee; though interestingly some including Oklahoma and North Carolina don't have any exceptions whatsoever. But they could probably change these laws before the electoral college meets if it comes down to it.
So the two avenues are, that in all scenarios you tell people a vote for Trump is a vote for Pence, so vote Trump. And either all of Trump's electors (or enough of them) vote for Pence and Pence wins, or the electoral college votes for a still-dead Trump and then, per the twelfth amendment, Pence immediately becomes President-elect given Trump's lack of life.
Given you're asking people to vote for a dead man so a live one can become President, I just don't really see it working.
I don't think that is as big a problem as you think:
https://www.washingtonpost.com/news/the-fix/wp/2014/10/01/five-people-have-won-election-to-congress-despite-being-dead/
