It does seem very likely that the amount of CO2 you produce for the rest of your life is greater than the amount produced if you dropped dead right now and decomposed. And if you always include the decomposition after death, living longer obviously generates more CO2.
I'm unsure about the rate, especially if nothing is done to slow the decomposition. Possibly you will produce CO2 and methane much quicker for a few days.
Serious note: CO2 from living sources that get all their energy from plants or animals who eat plants are not a problem, as this is a short-term closed cycle. But then you don't get to make funny jokes.