Technically plants do respire oxygen and produce CO2, its just that the photosynthesis process produces more O2 than they need, so its a net offset ๐ค
There have been experiments done since the 1800s proving that plants can survive in a closed environment, presumably by regulating the amount they photosynthesise, so there probably wouldn't be a global loss of plant life
The shadiness of the leaders aside, I've always thought that, with how prevalent PEDs are in competitive sports despite all the restrictions, it would be interesting to see how far humans can go if all restrictions are lifted