You could use the word reunite to mean people meeting again. You could say "When two people meet, one day they will reunite" or "If people meet one another, they will reunite" I would suggest saying something like "When two people meet, no matter what path life takes them on, they will always meet one another again" or "When people meet one another, no matter how far apart they may be, they will reunite one day" To be honest you could easily say "People who meet once will always meet again" Hope this helps