I would like to comment that this phrase "مع السلامة" means literally "go with safety". It is said as a "Goodbye" from the person staying to the person leaving.
And the answer is الله يسلّمك 'may God keep you safe'.
To be accurate, "الله يسلمك" is more of colloquial. Formally we would say "سلمك الله".
True, in theory. I've never heard anyone use that though.