The assumption that civilization(s) continue on planet earth for millions of generations means that after millions of generations it is still possible to live. Essential resources are still available, they have not been consumed by any previous generation.
Sustainable consumption means no consumption. No consumption in the sense that something is consumed i.e., no longer exists afterwards in a form that is retrievable with adequate means. No consumption of anything that is required for or contributes to life and that can not be done without.
When something is consumed, gasoline that is burned or aluminium that is thrown away, the matter it consist of still remains on earth. The form is less useful though, less energetic and more dispersed. It becomes considerably more difficult and expensive to retrieve in a useful form than obtaining new ones. If that weren't so, we wouldn't "consume" but keep it. So by preferring to use new sources, we make it more difficult for later generations to live. On the other hand, by gathering more knowledge and capabilities we make it easier for future generations to be. If it was certain that the second outweighed the first, consumption would be justifiable. To be in line with the assumption it would have to be certain. The knowledge we currently gather wouldn't seem to qualify, and even if it did, use rather than consumption would be safer.
Nature's cycles for e.g., carbon, oxygen, hydrogen and water, show how use that allows re-use for billions of years is possible. These cycles seem robust and contain very relevant elements. Hydrocarbons form the basis for life and make up a lot of our products and can continue to do so as long as these cycles keep operating. The various forms of carbon (graphite, nanotubes, fullerenes, diamonds) as well as hydrocarbons can assume very diverse properties. And there may be many other possible cycles that can continue.
Use can continue as long as cycles for the respective materials operate at adequate speed. Life can be good. If civilizations manage to stay within these cycles.
There is no future for consumers.
Future exists for users only.