I am sorry...but leaving him in the cup probably would not have helped.Maybe I should of left in cup
He just wasn't meant to be.
Looks like there is some stuff on his lower belly....I am going to take a wild guess and say that he might have hatched with a yolk sac infection and there is nothing you could have done to save him.
ALSO...98 is way too hot for a brooder.
Start at 90 in the future...and lower the temp each day.