The Roman Empire during Pax Romana largely turned away from context and had the most peaceful 200 year period in European history. Although the western empire eventually whittled away a couple hundred years later, there was no spectacular collapse and one could argue that the imperial system was atleast somewhat sustainable

I think you're going to need to clarify your terms. "Sustainability" is popularly used in the environmental context to mean that a given resource can be replenished (solar power), which is in contrast to those that cannot (fossil fuels). How that term applies to societies and governments is not clear.

Are you asking whether any empire has ever relied on purely sustainable resources? Are you asking whether any government has sustained itself to the present day? Are you asking something else?