WordNet (r) 3.0 (2006):

die out
    v 1: become extinct; "Dinosaurs died out" [syn: die out, die
         off]
    2: cut or shape with a die; "Die out leather for belts" [syn:
       die, die out]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "die out":
   be annihilated, be consumed, be destroyed, be gone, be no more,
   be wiped out, become extinct, burn out, cease, cease to be,
   cease to exist, dematerialize, depart, die, die away, disappear,
   dispel, disperse, dissipate, dissolve, do a fade-out, dwindle,
   erode, evanesce, evaporate, exit, expire, fade, fade away,
   fade out, fizzle, fizzle out, flame out, flee, fly, go, go away,
   go out, hide, leave no trace, leave the scene, melt, melt away,
   pass, pass away, pass out, perish, peter out, retire from sight,
   sink, sink away, suffer an eclipse, vanish, vanish from sight,
   waste, waste away, wear away