if a sim is not able to care for itself and the player does not help them, the sim will die. for example, sims will die from starvation if they don't eat. usually, they will die in accidents or from old age. when a sim dies, the grim reaper will come to take away the sim's soul. before the grim reaper takes away the dead sim's soul, other sims are able to beg for the dead sim's life. this will not always work. if it does, the sim will come back to life. if the sim really dies, they will be replaced by a gravestone or urn.