Complex sentence: If a person falls down then they may fall sick or die or his relatives may have the similar ill luck within a year and if nobody falls down, it is considered to be a good omen for everyone in the village.
Split into simpler sentences: If a person falls down then they may fall sick or die or his relatives may have the similar ill luck within a year. If nobody falls down, it is considered to be a good omen for everyone in the village.