Fig.: to suffer defeat; to fail to succeed; to die. Literally: to fall face down in the dirt

It's a very reassuring movie with the typical happy ending: the boy gets the girl and the the bad guy bites the dust

È un film molto rassicurante dallo scontato lieto fine: il buono conquista la ragazza e il cattivo morde la polvere

I just finished reading an exciting thriller: captivating, high adrenaline, well written, suspense up to the last page and, at the end, with a great twist of the plot, the bad guy bites the dust

Ho appena letto un bellissimo giallo: avvincente, adrenalinico, scritto bene, suspence fino all'ultima pagina, e alla fine il cattivo, con un grande colpo di scena, ci lascia le penne

Once again, the undefeated champion wins the nth challenge and another contender bites the dust

Ancora una volta il campione, tuttora imbattuto, vince l'ennesima sfida e un altro contendente morde la polvere

Although this cliché was popularized by early American Western movies of the 1930s, in which both cowboys and Indians were often thrown from their horses to the dusty ground, it is much older. It comes from the 1878 translation by William Cullen Bryant of Homer's Iliad. Here Agamemnon prays that he'll be able to kill Hector:
May his fellow warriors, many a one,
Fall round him to the earth and bite the dust