From what I gather when I can lurk, Pelosi, being 3rd in line for president, if something were to happen while she was out of the country....please extrapolate the rest. LOL
IF both the President and VP are incapacitated or killed, the Speaker of the House would be sworn in as President, her aircraft designated AF1 and she would be flown back to DC to take to make a speech.
But they would have to get both Trump and Pence at the same time. If Pence takes over, Pelosi would remain Speaker of the House and Pence would appoint a new VP....
...as I understand it from High School civics I took over fifty years ago.