I wish James would return, but I feel like DPC got the timing of his return wrong. Bringing James back in EP.12 is too late for any impact on the plot. In EP.12, Bella will most likely drop an 'L-Bomb' on the MC, thus burying all the fears she has about moving forward with someone she's hopelessly in love with (MC). James returning at the end of EP.12 would mean he'd automatically lose – zero chance of him having any chance with Bella.
The scenario would be different if James returned at the end of EP.8. In that case, it would also be bad timing, and Bella would hardly choose the MC over James since she have many uncertainties about a romance with the MC. This would mean an automatic loss for the MC at the end of EP.8, just as EP.12 would be an automatic loss for James.
The right timing was for James to return at the end of EP.11 – the final scene should have been James ringing the doorbell and Bella answering with a shocked expression. This would allow both the MC and James to have fair chances in EP.12, as Bella would be confused and wouldn't have said the 'L-Bomb' yet.
The MC could then make things easier by mentioning Zoey's return and that he'd like to rekindle what he had with Zoey (for those who choose Zoey over Bella), while the MC, who remained faithful to Bella and intended to have something lasting with her, would show himself as a bigger man, seeing himself as an intruder in James and Bella's relationship, leaving the scene so Bella wouldn't have to choose between him or James.
Obviously, with the MC 'out of the picture', Bella realizes she doesn't want James back in her life because he's not the one she loves, but the MC. When I say 'with the MC out of the picture' I'm not saying Bella should go back to James and then change her mind after a few weeks (no NTR, please). I'm referring to the MC letting Bella move on with her life, showing understanding of the situation. DPC would give the MC an awesome development, it would be a contrast to how the MC behaved when he found out about Josy and Maya (total snowflake) and it would also make Bella's declaration of love more impactful.