I'm fine with the idea of the heroines not returning--Bond's personal life is one of impermanence. There are only a few recurring characters in the books--M, Moneypenny, Loelia Ponsoby, Mary Goodnight--and they're connected with his work, his only source of stability (the only exception is May, but she's a servant). Even Bond's few recurring friends--Mathis and Felix Leiter--are work friends. He's with them only on assignment. True, the Bond girls are also encountered in the line of duty, but they usually have no reason to pop back into his life. If they did, they would jeopardize the life-work balance.
However, it is fun to try and imagine what happened to the Bond girls after their run-ins with OO7. In some cases, Fleming lets us know: Honeychile Rider had two children by the Philadelphia doctor who fixed her nose. Tiffany Case lived with Bond in his flat until she met a Marine at the US Embassy and sailed back to America to marry him (I bet the marriage didn't last). Gala Brand was of course engaged to Detective-Inspector Vivian--I presume that after she got married and had kids she probably retired from the Special Branch to become a housewife, as women often did in the 50s.
As for what happened to the other Bond girls, here are my guesses.
Solitaire: moved to Las Vegas and opened a psychic shop, telling superstitious gamblers' fortunes.
Tatiana Romanova: relocated by the Secret Service to Canada, where she met and married a Mountie. Had lots of kids.
Pussy Galore: having evaded prison, she moved to Nevada and opened the world's biggest whorehouse.
Judy Havelock: returned to Jamaica to rebuild and manage "Content," her parents' estate. Now a major banana exporter.
Liz Krest: inherited her late husband's millions and spends her days sailing around the world, collecting boytoys.
Domino Vitali: resumed her kept-woman ways, romancing rich playboys, until she married a wealthy count in Naples.
Vivienne Michel: continued her journey on scooter until she reached San Francisco, where she opened a coffee shop in Haight-Ashbury, giving poetry readings for hippies. Never married.
Kissy Suzuki: resumed life as an Ama diver in Fukuoka and raised Bond's son Taro, who after a scapegrace youth grew up to be a policeman on the mainland.
Mary Goodnight: took over her late boss's role as head of the Jamaica section of the Secret Service.
Trigger: executed by the Soviets for her failure to kill British agent 272.