From the guidance manual:
4.290 Any amount paid into a bank account after the claimant has died is made under a mistake of fact. The mistake being that the claimant was not entitled to that payment, because their HB should have terminated on their death.
4.291 Once an account provider becomes aware that a claimant, holding a sole account, has died they should return any credits received after that date.
4.292 LAs should take immediate action to contact the account provider for the return of any credits paid into the account after the date of death.
https://hbinfo.org/wp-content/uploads/guidance/hbopg-rec-op.pdf
4.291 suggests that this only applies to payments made after the bank is aware of the claimant’s death.