I still think RB had a specific reason for MB to change her name and initials to match his FNR. A dangerous deal/transaction. Needed ID proof of name…. A used/stamped passport more convincing than new/untraveled. None of his other known victims were asked to change their names. I think he intended to scam her and take her money like he did/tried to with the others, but also think in MBs case he needed to send her into a situation to finalize a big scam…… maybe the person he was scamming knew him as another name so he couldn’t access money under his FNR alias. Still something significant here to uncover I’m sure.
IMO, Marion's return trip to AU was unexpected (to her) & she intended it to be brief. She had kept her relationship with RB secret up until that point, so to tell her family she had returned to AU would have required a lot of awkward explaining. From Marion's perspective, she was working on establishing her new life with RB overseas before reaching out to family to say she had met someone & all was great. I don't believe she wanted to disappear, but just wanted to avoid criticism of running off with a man.
While she was in AU, she probably was just mostly waiting around while RB flitted in an out on "business-related" tasks. She probably took advantage of down time by tying up loose ends (trip to the eye doctor, cancelling car insurance) --all the while thinking she & RB would soon return overseas. On Oct 15, RB was able to get access to her money. I don't believe she was alive very long, after that date because everything related to Marion abruptly ceases (no more passport, bank, Medicare card etc.), despite there being a fair amount of activity before that.
It's possible that RB just disappeared leaving MB in complete despair and suicidal. BUT I think there are some clues that's not the case. The fact that RB got rid of his FR driver's license and never traveled on the Japan airline again suggest he was making efforts post-theft to distance himself from Marion. BUT, importantly, these changes don't actually distance him from Marion in any effective way. They are useless acts of desperation. He took proactive steps to commit the fraud (use fake name, never reveal his address). These post-theft, reactive steps, i believe, suggest something happened beyond his planned thieving.