It would look exactly the same, the 3D models and textures are what's behind the game's look, not the engine. And the 3D models and textures wouldn't change just because the engine change. The artists are behind the game's art design, not the programmers.
Nooooooot quiet. It's both, actually. The exact same models and textures can be handled a thousand different ways depending on the engine, each giving a unique look. Look at TF2, for example; most of those textures are solid colors, but due to the shading system in the
engine they are brought to life and look pretty darn good. That game would look like utter crap if it was in an engine without the special things Valve has set up.