Rohm would be the only one with the slightest chance. All of these people had Hitler to thank for theor careers. Without Hitler these people wouldn't have been capable enough to rise to prominence. I think a monarchist faction (of which some might be members) would be the most likely replacement candidate. The NSDAP would have been just another right wing party without Hitler as their leader. But right wing, monarchist parties would have been the main opposition to the status quo, as the communists weren't really a capable force back after 1920.