The legislative history of the 20th Amendment says a person becomes "President elect" upon a majority of the Electors voting for him. So Trump is now President-elect. If Trump had died after Election Day but before today, the Republican Electors would have been free to vote as they wanted.
This scenario almost happened to FDR in February of 33a month before the inauguration. A guy shot at him, but missed, killing the mayor of Chicago. People were afraid that Hoover as the electoral college runner up would be re-elected. So they passed the 20th amendment.
The 20th Amendment was adopted on January 23, 1933, before the attempt on FDR's life. Section 3 thereof provides that if the President-elect dies, the Vice President-elect becomes President on Inauguration Day. So if FDR had been assassinated, Vice President-elect John Nance Garner would have become President on March 4, 1933 (the date changing parts of the amendment took effect on October 15, 1933).
The 20th Amendment was adopted on January 23, 1933, before the attempt on FDR’s life.