What happens to Mildred?

We are unaware of what happens after Mildred leaves her home in the taxi. Montag imagines his wife was killed in the bomb blast.

The first bomb struck.

"Mildred! "

Perhaps, who would ever know? Perhaps the great broadcasting stations with their beams of colour and light and talk and chatter went first into oblivion.

Montag, falling flat, going down, saw or felt, or imagined he saw or felt the walls go dark in Millie's face, heard her screaming, because in the millionth part of time left, she saw her own face reflected there, in a mirror instead of a crystal ball, and it was such a wildly empty face, all by itself in the room, touching nothing, starved and eating of itself, that at last she recognized it as her own and looked quickly up at the ceiling as it and the entire structure of the hotel blasted down upon her, carrying her with a million pounds of brick, metal, plaster, and wood, to meet other people in the hives below, all on their quick way down to the cellar where the explosion rid itself of them in its own unreasonable way.

what is happening here and what is ildred realizing