The phrases in this excerpt that help to reveal the meaning of the word "blight" are:
The meaning of the term Blight is scourge, whiter, disaster.
The support of the meaning in the excerpt is "the last bitter hour": the final moments when someone is going to die.
“stern agony, and shroud, and pall": the end of a life using dramatical terms.
"breathless darkness": a kind of disaster that is coming, not to be avoided that paralyzed people.