I can’t do without tobacco.
If “farcela” means “do it”, should the translation be something like: “I can’t do it without tobacco”. For example : " I can’t write my novels without tobacco, my creativity depends on it". I think I know: “farcelo” is “do it”. I am confused.
Indeedy, “it” would make quite a difference. 
I think it depends on context. The sentence can be interpreted as “I can’t manage without tobacco” or “I can’t do it without tobacco.” Reverso Context has examples that reflect both usages.
Another way to translate from English, could be “Non riesco a stare senza tabacco”.
“Farcelo” is not a word, sorry! 
“Farcela” can be split as “Fare+ce+la”. When conjugated, it changes quite a bit: “Io ce la faccio”, “tu ce la fai”…
It derives from “fare” (to do), but has its specific meaning of “being able to do”, “manage to do”.
Edit:
Duh! When answering above I was fixed on the sentence at hand, and I didn’t think straight.
Actually “farcelo” can be used, just not on its own:
“Non riesco a farcelo stare” means " I cannot manage to fit it (somrthing) in it(something else)".
In this case it is even easier to assign meaning to the components: “fare” (to do/make) “ce” (in it/indirect object) “lo” (it - direct object). But it is part of a composite with stare: “far stare”, as in “make something fit”.