Most of the carbon on this planet is locked up in carbonate rocks, and not in the atmosphere or fossil fuels. Even if you burned every last bit of hydrocarbon fuel you could get your hands on, you could never bring the atmospheric CO2 back up to prehistoric levels. That is plant food locked up and out of reach, the remains of a much greener, livelier, warmer earth.
I've been saying this for years. Nobody seems to get it, not even on the anti-AGW side. If they did get it, it would be a centerpiece of the argument that CO2 can't possibly destroy the planet.
At the rate we are burning fossil fuels, we have hundreds or even thousands of years before we would burn the known reserves. That doesn't include the unknown reserves that are undoubtedly out there in the vast planet, some/most being under the seas.
So our CO2 add back to the atmosphere is exceedingly slow compared to the quantity of carbon available in the fossil fuel inventory. And by the time we would have depleted the fossil fuels that currently exist, more would have been formed by natural processes on the global scale of the carbon cycle.
There is nothing to worry about...use fossil fuels and forget this ridiculous carbon sequestering nonsense. It is a cost for nothing and as you point out, it converts carbon to a form that is a dead-end of the carbon cycle if it is successful.
They like to say we are using the natural resources unfairly, depriving future generations. Well, killing the carbon cycle IS depriving future generations.