Ah I thought so.
Strangely enough TG2 "thinks" you're still using the deleted render node and logically a camera is not attached to it, since it doesn't exist anymore.
I don't know if this would really qualify as a bug or if it is expected behaviour.
Disconnecting the camera from the rendernodes, reconnecting them and then reset the 3D preview and it should be back to normal.
Cheers,
Martin