The final chapter of Star Wars: Thrawn gives me the distinct impression that something has happened to the Grand Admiral. There's talk of his legacy. And Eli is reading a journal that's never mentioned directly in the book (but is clearly the source of the introductory paragraphs of each chapter). This combined with the talk of legacy, makes me think that Thrawn has passed away, and Eli has received instructions and a journal as part of some sort of last will.
The meeting where Thrawn is promoted to Grand Admiral doesn't bode a quick death for him, but seems to have happened fairly quickly after the defeat of Nightswan. Also, I haven't seen the last season of Star Wars: Rebels yet, but I know he plays a role there. So, if Thrawn has indeed fallen, I think considerable time must have passed between him becoming Grand Admiral and Eli reading that final paragraph.
Is Thrawn still alive then? How much time is likely to have passed since his promotion? Years? Months? Days?