He would upstage her in a heartbeat. He'd become the star and she'd immediately go back to being second-banana. The very last thing she'd want.
Rather, “if” Bill were to become an “Ex-president-but-married-to-the-current-President” HE would immediately be limited and ham-strung in HIS appeal and HIS ability to live high on the hog internationally as an international jet-setter (er, playbay/sex-god-in-all-but-name) and international fund-raiser.
BILL is the one who would “lose” if Hillary becomes president, and BILL (I think) has sub-consciously been fighting for her to quit/lose/get beat.
Now, he can get all the attentiona and applause and international money he could ever want, BUT IS NOT ACCOUNTABLE for ANYTHING he says or does or promises. Once Hillary becomes president, HE will be both noticed (since he is, after all, setting policy and international decisions by those words) and will be able to be held responsible for what he says and who he says it to.
Now, Obola and Hillary and Biden don't care. They will get as money and headlines as they want - and the press corpse will keep giving it to them as they EVERY decision by a repubbie president and a repubbie congress. But I think Bill - for all his failts - does care.