We shouldn’t need to count on voters dying to avoid outcomes like this. Our institutions are broken if they can’t protect the public from a mentally ill public official on a power trip.
If they voted for Trump it doesn't mean they agree with him on immigration and crime. They just have to think it's less important than the positions they do agree with. An effective argument to win over those voters isn't "you're evil and should have better opinions," it's "immigration policy is important too and this one is really bad, plus Trump is doing a bad job on your pet issues."
Swing voters exist. Moderates exist. Single-issue voters exist. Occasional voters exist. These are observable facts about the world.
The four groups exist in large enough numbers that they decide elections. Die-hard party loyalists exist, committed non-voters who'll never ever vote exist, but they're fixed quantities and are practically irrelevant.
I agree with the statement that what really matters is whether you can convince someone to vote differently - but, yes, of course you can! Trump has run three times and only won twice. Obviously there's something that can convince people not to vote for Donald Trump, because it has already happened.