A sustainable vegetable garden signifies one that can be sustained over time, and would always entail I) growing food you wish to eat, so you’re motivated to keep on growing, II) growing efficiently, so it is worthwhile , and III) taking care of environmental problems, so the earth will continue to encourage growing.
Following that, look at using heirloom seed as opposed to hybrid, if you’re extremely worried about losing the ability to substitute seed annually from commercial sources. However, saving and growing your own seed is hard and time consuming. A superb reply to this issue is the Garden In A Can heirloom seed offered by Mountain Valley Seed Company (Rat droppings). Other seed companies might have something similar. I suggest that you get a can of the triple-sealed seed, keep it against the potential catastrophe, and then buy and use the very best seed you can buy and do not be concerned about trying to grow for and save your own seeds.
A household could be self sufficient in their food needs from appropriate 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 damaging the land, but instead should enhance the land, so it will continue to encourage healthy plants indefinitely. Therefore, pesticides and herbicides should be used very judiciously, and where possible these issues should be managed by cultural practices as taught by Dr. Mittleider for example 1) removing all weeds in the garden area, 2) watering just the plants’ root zone, 3) starting plants in a protected environment for a quick, healthy and robust start, 4) feeding plants appropriate quantities of balanced natural mineral nutrients to guarantee fast and healthy development, 5) harvesting all plants in maturity to avoid allowing pests and diseases to multiply, and 6) shedding any insect or disease infested plant parts from the garden, and integrating healthy plant components to the soil to improve soil structure.