Can chronic venous insufficiency (fluid retention in lower legs) be reversed or it never reverses?

Usually yes: Cvi occurs when there is pooling in leg veins, causing leg swelling, inflammation, & ulceration. The most common cause is when the one-way valves don't work well, leading to venous reflux, or back flow, with blood pooling in the veins. This can result from genetic predisposition, pregnancy, injuries or blood clots. See a vein specialist for a proper evaluation. Treatment often very helpful.

Venous stasis : Venous insufficiency can be controlled medically with compression and some simple preventive measures. Venous insufficiency, if deemed severe enough due to complications (like ulcerations), can be treated with surgery. Even with surgery, complete correction, from the pure sense of the word, is not the correct language. You would still have compression stockings recommended after the procedure.

Depends: Whether fluid retention in the legs due to chronic venous insufficiency (cvi) can ever be reversed with treatment or not depends on the cause and severity of the problem. If the cvi is due to a previous deep vein thrombosis, it is possible that the swelling might never completely go away. On the other hand, if the swelling is due to varicose veins, treatment should be quite effective.