There are reports that as early as 1929 Dengel was forced by serious illness to cut short a Comintern mission overseas. There is no indication that he became more actively involved in party work after his return to the Central Committee ten years later. A further brutal diplomatic realignment emerged on 22 June 1941 as the German army launched a massive invasion of the Soviet Union in breach of the dictators' non-aggression pact. That same day, Philipp Dengel suffered a serious stroke from which he would never properly recover. In 1944, he was listed as a member of the Soviet sponsored National Committee for a Free Germany, but he was no longer playing any active political role. It was as an invalid that he returned with his wife to Berlin in September 1947. He died there six months later.