NorthWest Biotherapeutics Inc (NWBO)

[CherryTree1]

Your underlying assumption is that his move to Merck was his own initiative and was not done in partnership 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?

He may have simply been asked by Merck to make a temporary move to NWBO to help them navigate the regulatory hurdles. If he already knew many of the FDA folks from his work at Merck they might be more receptive to him, but that would only be the case with him working for NWBO not as a 3rd party still working for Merck. It could very well be that he has accomplished what he was asked to do and that would also explain why he is returning to what appears to be essentially the same position at Merck. That's my 2 cents.