I'm not a medical doctor but I'm still going to pretend like I know what I'm talking about:
I feel like there's a couple ways you could die, renal failure, maybe burn a hole in your throat and die of some complication thereafter, or like that one kid who drank too much water which caused his brain to swell and herniate. You could also die from a caffeine overdose but I'm not sure how much caffeine is in coke and it depends on your body weight as well
Suffice to say it'd probably take some serious willpower to kill yourself by drinking a forgetload of coke.