Without debating any pros/cons for Bill Clinton: He'd likely be called "Former President Clinton". Any living past-president is bestowed the title "Mr. President", even after they leave office (Or I guess "Madam President", if that's how it plays out in November). Obviously if Hillary is in the White House, it would be confusing if Bill continues to use "Mr. President", as he is entitled to do currently.
Without debating any pros/cons for Bill Clinton: He'd likely be called "Former President Clinton". Any living past-president is bestowed the title "Mr. President", even after they leave office (Or I guess "Madam President", if that's how it plays out in November). Obviously if Hillary is in the White House, it would be confusing if Bill continues to use "Mr. President", as he is entitled to do currently.