Q: My truck had no oil so the engine started knocking but I only went maybe a half a mile down the road is my engine ruined

To answer your first question, "Is my engine dead?", I would fix the leak, add oil and see if the truck runs and if it runs, see if there’s any noise. If the engine does run, and there is no noise, if you’re curious about some principal measures of engine "condition", you can measure cylinder compression and oil pressure. If cylinder compression is reasonable, the engine runs well and has oil pressure, and there is no noise, the engine is not dead. If the engine turns out to be "damaged" (noise, etc.), options are: 1) rebuild what you have; 2) install a used engine; and 3) buy a re-built long or short block. If you want the diagnostic steps referred to above performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a no start diagnostic and the responding certified mechanic will inspect what you have and then advise you as to the least cost option if you end up needing repairs. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.