Part of my sphere disappears when in BGE I'm trying to make a skydome but before I even added a texture to the spear I wanted to see if it was there when I started BGE. Part of it was gone!

can anyone help me?
Only switch of backface culling when you need to see both sides of the face at the same time and both sides should have the same material (it doubles the faces!). Use cases: glass, leaves, paper, curtain

In your case you ALWAYS want to see the inner side of the half-dome. This means you model is incorrect as you can see the outside only. To change that go into edit mode and flip the normals w.