Do we want to make it so that a terminal can be unavailable?
The main case I see for it is if we have a block that has a codomain but our processor is not using it for one reason or another.
I lean slightly towards yes it would be useful.
One way to do this would be to have a built in processor called Termination processor or something and make it so you can wire up a terminal to it through a wire. In graphics maybe it would show an X over the terminal in the graphic?