Therefore, after his death only Aikido techniques remained and the teachings of the spirit which were the ultimate objectives of his quest, and which he found so difficult to explain, disappeared completely from the minds of his devotees."
This is simply not the case... Sunadomari Sensei, Abe Sensei, and Hikitsuchi Sensei were quite serious about understanding Aikido as it was outlined by the Founder. Each created a training system which was designed to pass on this knowledge to his senior students.
Yamaguchi Sensei, for example, looked for other ways to understand the spiritual side of Aikido and while not involved directly in the Omotokyo practice was involved with George Osawa as were many of Yamaguchi Sensei's students. These spiritual investigations were certainly inspired by the Founder's teachings about Aikido.
Imaizumi Sensei and Chiba Sensei chose to pursue Zen training as the way to develop their spiritual understanding. While not the same Path as outlined by the Founder himself, they were inspired by those teaching enough to develop this spiritual practice for themselves.
Saotome Sensei's first big project when he got to the United States was to write Aikido and the Harmony of Nature in order to make the spiritual teachings of the Founder comprehensible to modern people lacking in the Shinto foundation which the Founder had. His experience of the spiritual aspects of O-sensei's teachings effected him very deeply.
These are only the folks with whom I am familiar. I would venture to say that, regardless of what form their transmission of Aikido eventually took, the teachings of the Founder were NEVER out of the minds of these devotees. It isn't just about the physical technique for any of these teachers.