Hennig's mother was a deaconess at her marriage and his father had a doctorate in the psychology of religious perception and was an ordained minister, though he had chosen to become a high-school religion teacher rather than a pastor.
Apart from increasing his difficulties and in particular excluding his obtaining university posts in a Nazi-dominated society, the marriage also definitively put paid to an ecclesiastical career in the Lutheran Church.
Meyer was also a German patriot and one of the Jews who refused to believe that the rise to power of the Nazi party constituted a danger, to the point that he even returned to Germany in 1938 after a journey to the United States with his wife.
Managing to have it retrieved by a paid messenger, and forced then to leave his family behind for the moment, he first landed on the English coast at Folkestone and then headed via London through England and made the sea-crossing to Ireland on 6 October 1939.
Though formally neutral and in various respects pro-German, the Irish Free State was an impoverished country and wartime conditions made it difficult for the foreigner Hennig, though a Catholic with a reasonable grasp of English, to make a living.
He was subsequently joined by his family in November 1939 and together they began their Irish life, with its twists and turns of good and bad fortunate as they found congenial accommodation in a cottage with a garden at Sutton to the north of Dublin, but the wife and children went down with whooping cough and other health problems soon after their arrival.
The earlier years were made easier by the friendship and social acceptance of a number of other German-speaking exiles, such as Erwin Schrödinger, an Austrian Nobel prize-winner for Physics, the medievalist Ludwig Bieler and the bacteriologist Hans Sachs.
Neither young nor fit, but a man of considerable character, Felix Meyer took up the cause of other Jews in Belgium, playing on his standing with Belgian industrialists to obtain medical supplies for prisoners, and with sheer bravado even complaining to high-ranking Gestapo officers about the legality of some of the detentions, Often, he was able to exploit the fears for civil unrest or for postwar personal retribution of the components of the military government in Belgium, and not rarely he played off Gestapo and German military against each other, obtaining the release of prisoners or at least improvement of their conditions.
In late 1946 Hennig was glad to accept a job as a clerk with the Bord na Móna (Irish state peat-extraction enterprise) at a somewhat isolated location at Newbridge, County Kildare, 40 miles from Dublin, where he was obliged to lodge during the week.
From there he found a similar job with the state electricity company, but this time at their central office in downtown Dublin, which reunited him with his family and gave him ready access to the city's libraries.
Hennig's literary output in Ireland included many newspaper and magazine articles, mostly short, many couched in the style of popular journalism, but all betraying his very serious academic formation and abilities, a lively intelligence, an enquiring mind and a committed and reasoned Catholic faith.
While less stressful than the paid employment he had known in the postwar years in Ireland, it was a humdrum task in which fundamentally had no interest, but it ensured his family's financial stability and was seen by him as a duty to the memory of his revered father-in-law.
In 1967 he was made an Extraordinary Member of the Abt-Herwegen-Institut für Liturgische und Monastische Forschung (Abbot Herwegen Institute for Liturgical and Monastic Research) of Maria Laach Abbey, near Bonn.
Despite the initial difficulties in gaining local acceptance in the somewhat clannish Basle society, Hennig did benefit from the renewed possibility of publishing in German and from the residence in the city from 1948 of his friend Jaspers.
Hennig's work, dispersed in many different publications, was in part brought together in various retrospective collections: His privately published autobiography is a story of experiences and opinions rather than dates: