If you must stand for long periods, walk on breaks or sit and raise your feet. Avoid tight shoes and high heels. Also, don't choose underclothing that fits tightly around the upper thigh. Such clothing will increase the resistance to blood flow. If, despite the best efforts on your part, your veins get worse, surgery to remove the larger superficial veins is an option.
Venous blood has a number of options.
The blood will simply be rerouted through the deeper veins. The Detroit News.