So, say McKinley dies shortly befor the Republican convention in 1896, and Bryan goes on to win. Who would be the likely Republican candidates in 1900?
Well looking at the other candidates for the nomination in 1896 would be a start. It appears Thomas Reed, the speaker of the house, was the runner-up in delegates, although McKinley was nominated on the first ballot and must have been greatly preferable. Some of the other candidates include Matthew Quay of PA and Levi Morton of NY (the most important swing state).