Science Fiction

Could be and probably is a fakeout. Tellem just wanted to put Seldon through that to wring whatever she could put of his mind. So in that sense the deathbed flashback trope was actually a literal plot point. It wasn't just us seeing those things, but Tellem. Maybe she'll learn something that changes her mind about Seldon.

In fact, I think whoever gave him a body again did it for exactly this purpose. A holo-Seldon would not have been vulnerable to Tellem, and thus wouldn't have succeeded in eventually winning her over. The whole resurrected Hari gambit is a strategy to win over the Mentalics.

Plus if they really were going to kill Seldon (again), they wouldn't have used it as a cliffhanger. They would've just killed him.

I thought it was more alluding to the secret that the Mentallic leader pulled out of his memories. We hear that he’s ashamed of something and not as perfect a man as everyone thinks he is and only find out what happened as his “dying” thought.

Plays well with Salvor theorizing that he was brought back to life to have some flesh in the game and him debating killing himself with the scientist during the stampede but deciding not to. He had a reason to live (and kill) before, so why not now?