If i were going 10 mph when my timing chain broke on 1998 Nissan Altima is engine shot?

Not necessarily. If the timing chain breaks while the engine is running, it can cause the valves to hit the pistons, which can then damage the engine's cylinder heads, pistons, and connecting rods. However, if you were only going 10 mph when the timing chain broke, it is possible that the engine may not have been damaged as severely. It is difficult to say for sure what the extent of the damage is without inspecting the engine, but it is possible that you may be able to get away with replacing just the timing chain and tensioner.