I agree she'll be a candidate again by 2020 but I think she is more likely to be a candidate for a liver transplant than a candidate for President.
I heard that she graduated from wine to hard liquor since her defeat at the hands of Trump in 2016. She is not in good health, she's prescribed multiple medications and the alcohol isn't helping. Or so I heard. (Source was a Clinton author who was interviewed on WOR. I don't recall the author's name but it will probably come to me as soon as I post this. He was touting his new book.)
The author I heard talking about Hillary’s health and drinking was Ed Klein.