This is more a camera issue. Some cameras support fencing or area limitations whatever sounds better for you. I use the Canon C700 and there are a lot of definitions possible where the cam should go and what to do if this and that.
vMix just controlls the camera and has no information of it's relative position. This is something only the camera itself could know.
If the camera doesn't support it natively the camera can be tracked with various solutions as well. But they come with a heavy price tag and add even more requirements.
Or you use a software in combination with other sensors to limit the movement. I have Stage Precision in my mind.