The only acceptable synonym of sustainability (noun) is our survival.
Our survival is the very essence of the definition of sustainability. Using the synonym in a sentence very well retains its intended meaning.
Fossil fuels do not support our survival very well because they are a limited resource that will eventually run out.
Have we underestimated the importance of our survival?
The idea of trying to promote rapid economic growth for the benefit of humanity is entirely alien to the supporters of our survival.
Without a doubt, our survival is the ideal synonym of sustainability and can be used interchangeably.