Thinking on it - the helmet message of what else is he not being truthful about?
It makes a bit more sense that they are bringing in a replacement for his position rather than appointing an interim chair. He has in fact tendered his resignation and administration has acted accordingly. He is telling his staff and colleagues that is just a sabbatical but he knows he is planning on never coming back - off to off himself by some means passive or active after he leaves.
Do we know if he has anything or anyone outside of work? The one connection we knew about, his father figure relationship, was last seen as toast. His father figure mentor died during Covid. Plan is to travel alone. Pretty sure there are some nice steep cliffs near his planned destination.