Although all of Donald Hersom's problems seem to have been published in the 1930s/40s, he was still alive in 2000:
A magazine we mention too little in these pages is The Problemist, the organ of the British Chess Problem Society. In the current issue, Sir Jeremy Morse contributes an article on the little-known problemist D.H. Hersom, who was active in the 1930s. Sir Jeremy was reminded, when he used one of Hersom's problems in a talk last year, that nothing was known about the problemist save that he was British. The BCPS Librarian, John Beasley, discovered that he was living in Barking, East London, in 1942. The electoral roll confirmed that Donald Henry Herson was at that address in 1939. Sir Jeremy then visited the Family Records Centre, where he discovered that Herson had been born in Ilford on 11/1/1914 and married in Bath in 1947, when he was living in Bishop Aukland. He found a Mr John Herson in the Durham telephone directory, who informed Sir Jeremy, to his immense delight, that his father was alive and well and still interested in chess problems.
In fact the wonders of Google have turned up Hersom's obituary, dated December 2006:
This also gives his full name: Donald Henry Hersom.