This completely sidesteps the issue. No one asked if the planet was alive. When an educated person says or hears "the planet", they should, unless context dictates otherwise, interpret it to mean the entire biosphere. This is a question of morality and fairness to all life. This anthropocentrist mentality is short-sighted and selfish.
And just because the sun expands in a few billion years doesn't mean I shouldn't be nice to my neighbor today.
Considering the Earth was much hotter and colder with vastly different concentrations of atmospheric gasses at given points in time than it is today, yes it is "sustainable". The planet and life at large do not give a damn.
The Earth will continue to orbit and spin and life will go on, until one day the Sun decides it's time to get fat and eat a couple planets.
As already mentioned elsewhere too, the Sun will eventually grow fat with helium and nom the planet along with a couple more.