Formal:
* Jusqu'à ce que nous nous rencontrions à nouveau. (This is the most literal translation.)
* En attendant notre prochaine rencontre. (This means "awaiting our next meeting.")
Informal:
* À bientôt ! (This means "See you soon!" and is very common in French.)
* On se retrouve bientôt. (This means "We'll see each other soon.")
* À plus tard ! (This means "See you later!")
Romantic:
* Jusqu'à ce que nos chemins se croisent à nouveau. (This means "Until our paths cross again.")
* En attendant notre prochaine rencontre. (This means "awaiting our next meeting.")
The best translation will depend on the specific situation and the relationship between the speakers.