If I drink coke zero during a fast, will this have any effects on the results long term?
It will create an insulin spike and interfere with your gut flora. If you want to read more, google will find you plenty of studies. Of course whether you choose to use artificial sweeteners is up to you though.
Yes. Technically, Coke Zero breaks a fast because your body may still release insulin in response to the artificial sweeteners. I used to drink it and when I started IF, I only drank it during my eating window. Eventually, I phased it out completely. It’s not good for you regardless of any diet.