I am Italian and, in this context,
"Ci vediamo. Bella!" (He meant that of my Italian by saying this I believe)
...Bella is not used with the meaning of beautiful but is somewhat alike to "Roger and out". With the same meaning, in Florence you will hear said Buona (actually pronounced bona, or exaggerated in bonaaaa). It's a very familiar form of arrivederci (see you) or ciao.
Not answering is acceptable, at least in Florence, but if anything you just reply with the same: Bella! (or bona!).
Bella lì is usually employed with the same meaning of "Good take!" in the film industry; it means that some idea, concept, or procedure is being approved. I usually employ it to stop someone from further working on something that (in my opinion) is now more than good enough. I could translate it with good, that's cool, perfect! or as I said, good take.
It is also used as a greeting, where it is synonymous with *Bella zì". You could then welcome someone by saying "Bella zì, come butta?" (Nice to see you, how's it hanging?). It is an extremely familiar and informal way of addressing someone, only ever used between friends.
I would most definitely not expect Bella lì in answer to Bella.