I don't expect to be, but if so, I'll let you know.
That example is probably better this way:
I don't expect to be [elected, represented, told, levitated, etc. etc.] but if I am, I'll let you know.
Do you like eating? If so, how about cooking? That sentence is fine. If so means: If you do.
As for that being said, it usually is used to set off a thought or thoughts after another one has been expressed. It would usually not follow a simple question. [Do you like eating? That being said, how about cooking?] In that sentence there is a question, which really doesn't lend itself to being followed by "that being said".
I like eating, especially in expensive restaurants. Eating at home is alright if my father cooks because he is a chef. My mother really doesn't cook very well and even burns the food!. That being said, I would not turn down an invitation to a fast-food restaurant because I really don't know what they are like.