Can we just buy one way tickets for now?

We will be getting our residence permits renewed for one more year soon, and then returning to NZ for a holiday. When we buy our tickets to come back to China for another working year, can we just buy one way tickets to China, or do they need to be return tickets? We don't know where we want to fly to, when we leave China at the end of next years contract, and so would like to keep it open at this stage.