They may still have the right to get their money back.
Sorry, they do not -- that's not how the law works in Singapore.
The only legal creditor claim against withdrawn CPF funds is for
new debt (if a creditor is so foolish to do that), incurred after the withdrawal. Also, an existing creditor may have previously decided not to pursue collection of the debtor's non-CPF (and other non-shielded) assets, as a gesture of goodwill or for whatever other reasons. The existing creditor might change their mind once the CPF member starts withdrawing CPF funds (subject to legal time limits and any binding relief agreements), but those
particular funds are not legally touchable in Singapore.
Even if the amount successfully bequest to your heirs, they do have the means to trace and might get the money back before it goes to your heirs.
No, those funds cannot be touched in Singapore, not legally. And if you're worried about an extra-legal misappropriation, there's the Enhanced Nomination Scheme.
Not sure if you can request the amount to be transferred overseas.
As I wrote, other countries' laws are often different.(*) Once you transfer any legally protected funds out of Singapore, all bets are off.
(*) But other countries can have similar laws, within their own borders. As one example, in the State of Florida (U.S.) there's a "homestead law" that protects primary private residences from creditors and court judgments. O.J. Simpson, the famous ex-U.S. football player and actor, who was acquitted in criminal court but found guilty in civil court of murdering two people, personal benefits from the Florida homestead law. The well-known U.S. "401(k)" retirement accounts are also legally well protected in that country, and "IRAs" are in many (but not all) states.