I fractured my hand and broke a small piece of bone of in the middle of my hand. The ER dr put me in splint until I saw the ortho, will this need surgery or a cast and the piece of bone can stay there?

Depends. On how big the fragment (piece) is. Small non displace fragments sometimes don't require any treatment. Very hard to answer you without seeing and xray. Don't miss your appointment.
X-ray. I do not feel that anyone here can answer that question without seeing the x-ray. If it is a "bone chip" (avulsion) then you probably will need nothing but splint. It really all depends on where the fracture is.
Depends. Without seeing an x-ray or knowing what is "broken off" it is impossible to know what is wrong with your hand/wrist ; therefore how to treat it. X-rays of "wrist sprains" commonly show a small fleck of bone on the top of the wrist. The fleck is significant only becuz that is where the ligament was injured. Remember wrist sprains can take as long to heal as a fracture.