Dr. Menon is in his mid-70's. He has done the work the company needed to be done. His area of expertise is in the earlier development stages, not bringing them to commercialization.

They hired Dr. Bertolino because he is experienced in getting drugs commercialized.

First Menon went to half time, now he's done, years beyond when most people retire. That seems logical enough, doesn't it? Phased retirement, kept on a bit longer than he was probably really needed, and now, when there is no work for him to do, he's no longer employed.