For a standard 5gal(18.9 litre) carboy fermented to 12% alcohol content by weight (not volume, 14.5% by volume) approx 1100 litres (264 gallons) of CO2 at 1 atm, 68F. But if you knew that, you would also know that 2.268 kg of ethanol had been produced allowing the simple math to calculate % alcohol by either weight or volume.
The prediction, assuming 100% conversion, is that each molecule of sugar produces 2 molecules of ethanol and 2 molecules of CO2. Using atomic weights 0.51 x weight of the sugar tells you how much ethanol you can produce. That ethanol weight divided by the ethanol weight + the weight of the water used will give you % ethanol by weight, you would then use the density to calculate % alcohol by volume.
One could use CO2 production by unit of time (measure how long it takes to collect a liter of CO2) would be indication of how active fermentation was, but it would not indicate (assuming a constant temperature and pressure) whether it was because you were a) running out of sugar for the yeast to consume, b) yeast was dieing off from alcohol concentration, c) yeast was dieing because of infection, d) yeast was dieing because of pH. Though over several batches of recording these rates, taking SG readings, pH readings, do yeast counts you would be able to use the rate of CO2 generation as an indication of % alcohol as well as an indication of whether your pitch rates were consistent.