The death of Tracy caused Bond to resign from MI6 out of grief.
- If you subscribe to the fan theory that James Bond is a code name and several agents have used it (explaining Bond's long career and changes in appearance caused by multiple actors), then it's possible that the grief over Tracy's death caused Lazenby-Bond to resign from MI6, or he was declared psychologically unfit to continue. This resulted in Connery-Bond returning to duty for Diamonds Are Forever before being replaced by Moore-Bond.
- Or, if you subscribe to another fan theory that Bond and Blofeld are both Time Lords, the stress could have triggered a regeneration.
- That or he committed suicide. After all, the movie begins with James stopping Tracy from committing suicide by drowning due to, among other things, the death of her spouse. Now Tracy is dead and there's a beach right by their car, and he does say "We'll be going on soon...."