A sustainable resource is a resource that is constantly renewed. For example water would be a renewable resource because of the water cycle.
Substainability
Hopefully the sun will go on shining for a few years yet
Do you mean - Sustainability?'Substainability' is not a English word.Sustainability (noun)The act/ability to sustain something (physical or mental).The test for the duration it can sustain for.From 'sustain'To keep up, experience (such as an injury), to withstand, to support, to confirm.
  Sustainable development is a pattern of resource use that aims to meet human needs while preserving the environment so that these needs can be met not only in the present, but also for future generations