From Epstein's point of view what reason would he have not to kill himself. He was NEVER going to leave that cell alive. He could drag it out for the rest of his natural life, or he could check out immediately.

I do think the guards knew/suspected he would do this and went out of their way not to interfere.

What motivation do you suppose the guards had if they "went out of their way not to interfere"?

To me it seems that such a choice on the part of the guards would amount to a serious dereliction of duty.

Why would they willful choose to do that?

I would assume you get a lot of shit protocol when an inmate kills themselves on your watch. Why would the guards be interested in that?