A sustainable vegetable garden means one that can be sustained over time, and would always involve I) growing food you want to eat, so you are motivated to continue growing, II) growing economically, so it is worthwhile , as well as III) taking care of environmental problems, so that the ground will continue to encourage growing.
After that, look at using heirloom seed rather than hybrid, if you are extremely concerned about losing the ability to replace seed annually from commercial sources. However, growing and saving your own seed is difficult and time consuming. An excellent reply to this issue is the Garden In A Can heirloom seed offered by Mountain Valley Seed Company (www.mvseeds.com). Other seed companies may have something similar. I recommend you get a can of the triple-sealed seed, keep it against the potential disaster, and then buy and use the best seed you can get and don’t be concerned about trying to grow for and save your own seeds.
II) Using the best growing practices, like those taught by the world-renowned Dr. J. R. Mittleider, (Rat droppings)assure you the greatest yield of healthy vegetables from the least space, and with the least amount of labor and financial inputs per unit of production. A family could be self sufficient in their food requirements from proper gardening of just a small portion of an acre, and this is the best proof of success in achieving a sustainable garden.
III) Gardening should always be done without injuring the land, but instead should improve the land, so that it will continue to support healthy plants indefinitely. Therefore, pesticides and herbicides should be used very judiciously, and where possible these issues should be handled by cultural practices as taught by Dr. Mittleider for example 1) removing all weeds in the garden area, 2) watering only the plants’ root zone, 3) beginning plants in a protected environment for a fast, healthy and robust start, 4) feeding plants appropriate amounts of balanced natural mineral nutrients to guarantee fast and healthy growth, 5) harvesting all plants in maturity to avoid allowing pests and diseases to multiply, and 6) discarding any bug or disease infested plant parts away from the garden, and integrating healthy plant components into the soil to improve soil structure.