take care; stay well
A warm, casual farewell used when parting from someone you may not see for a while. Often said to friends, family, or colleagues.
じゃあ、またね。元気でね。
Well then, see you. Take care.
遠くに行っても元気でね。
Even if you go far away, stay well.
またね is a very casual farewell used with close friends expecting a quick reunion, whereas 元気でね often accompanies a longer or uncertain separation.
ごきげんよう is an elegant, formal farewell used in polite or old-fashioned speech, while 元気でね is casual and affectionate.
From 元気 (げんき, 'healthy, well') + で (copula conjunctive form) + ね (sentence-ending particle). Literally 'be well, okay?', used as a set farewell phrase.