Perhaps you can switch to the die sprite animation (and set image_index to zero as well) when hpHero is zero, and in the Animation End event check if the sprite is the die sprite, and if so, game_restart().
You could set an alarm to restart the game after a certain amount of time, e.g. the duration of the death animation.
When hero dies:
if hpHero = 0
sprite_index = hero_die_sprite // set current sprite to death sprite
image_index = 0 // start at the beginning
image_speed = 1 // play at speed set in sprite editor
alarm_set(0, 180) //Alarm 0, 180 frames at 60fps = 3 seconds before alarm triggers