Well, I was responding to a question, which was, "What happens if Trump dies the day before the election?"
So at that point, there has not yet been an election. Anyone can still become President -- you or I could run for office and win. The Republican Party is under no obligation to keep Pence alone on that ticket. They could, and probably would, ask Mike who he wanted, but whatever the actual process was, the end result would very likely be Mike Pence for President and someone else on that ticket for VP, with that someone else being chosen by Pence in consultation with the Republican Party.
All this will have happened before the election, so there is no law against any of this. It's all 100% legal.
The legal questions would come after the election, because it would be too late to adjust all the printed ballots, which would all still say "Trump / Pence". Was it fair to the voters that the candidates were misrepresented? Should we have a re-vote? Should this, should that.
But ignoring those battles, Pence will then nominate a VP, just like Gerald Ford did in 1974. The Senate will confirm that nominee, and life will go on.
But notice at no point does any Speaker of the House enter into this equation. Pelosi, under the 1947 succession act, is next in line, but that's it. She gains no power whatsoever unless Pence also dies before he can nominate a VP. And FWIW, there are serious Constitutional questions about the Speaker even being allowed to try to be the President -- even if Pence died before he could nominate a VP, Pelosi's next-in-line status would be challenged before the Supreme Court and might very well lose, but that's another thread.
