If trump died before the Electoral Votes are cast, they wouldn’t be bound to vote for him and can vote for anyone, but its almost certainly going to be vance. Then either vance or RNC picks someone else to be the new VP to tells the electors to now instead of voting: [Pres: trump VP: vance] its now [Pres: vance VP: whoever they find to take this role]

If both trump and vance died before the electoral votes are cast, then RNC find 2 new people to tell their electors to vote for.

(Remember Electors are selected by their parties and are usually party loyalists that aren’t gonna vote for the opposing party. Think of people like Former President Obama being an elector in his state for the democratic ticket, he aint voting trump ever, and same thing with a loyal maga supporter, they aint ever switching to vote Democrat.)

If trump died after the electoral votes are cast, vance takes the oath and become 47th president, VP is empty. vance can appoint someone to be VP with simple majority of both houses.

If both trump and vance died after the electoral votes are cast, the speaker of the house, mike johnson, swears in as Acting President (after being required to resign as speaker of the house) for the rest of the term or until someone else above them in the line of sucession becomes available to be acting president. (We dont know what happens if acting president mike johnson nominates a VP since the new VP would be above him in the line of sucession)

Only VP takes the title of “President”, everyone else in the line of sucession is not designated by the constitution but is only statutory.