The idea of a permanent return could allude to the fact that Onesimus, being a Christian, would now faithfully serve his master and not run away again. More likely, it is a reference to the eternal fellowship that Onesimus and Philemon would enjoy seeing as they both belonged to Christ. A new relationship that transcends earthly relationships.1
15 Peut-être a-t-il été séparé de toi pour un temps, afin que tu le retrouves pour l'éternité,