I don't think it is the simplest explanation but certainly reasonable.
Another simple explanation is that he realized he made a mistake and talked with his old employer. Happened to me. I decided to take another job and my former employer approached me and asked me to come back. For a number of reasons I rejected the offer. I did not make a mistake and was convinced of the opportunity.
In Duffy's case, it is certainly possible upon entering the company and reviewing things first hand that NWBO was not the opportunity he thought it was. From his vantage point maybe the results were not anything to write home about and he was disappointed. Maybe he thought there were better opportunities with Merck.
If NWBO were pioneering a fundamental sea change in the way solid tumors are treated and the results were undeniable, why would you leave? How could Merck give him a better deal? If NWBO hits a home run as LP and LG have said a number of times, the share price should very greatly appreciate and he would be a significant part of a new paradigm in addition to being very wealthy. Wasn't that part of the reason he left big P to go with an exciting start-up company with a paradigm changing product platform? Surely he did extensive DD, at least as much as he was able being on the outside. Being on the inside could have changed his perception. Maybe he did not have faith in LP/LG' s commercialization capabilities. Maybe he found a hole in the science. Who knows and nobody is really telling beyond glib explanations.
His departure is a concern and I don't see that he was promoted upon return to Merck or that he received significant compensation that would rival what he could take in if NWBO is successful. With his background and being an insider he would have an excellent idea of whether NWBO had the goods. His departure certainly raises concerns. He does not strike me as a gambler and what looked good on the outside, upon further inspection while on the inside, evidenced, at least to him, that it was less than what he originally thought.
I just don't buy the simple explanation that he got an offer he could not refuse or that he was on a "mission" to validate NWBO. At least equally persuasive is that he did not like what he saw up close. JMHO.
