What is left over when water and sodium hypochorate decompose, i.e. household bleach?
It depends on temperature. At higher temperatures, hypochlorite has tendency to disproportionate: $$\ce{3 ClO- -&gt; 2 Cl- + ClO3-}$$ Otherwise it mostly releases atomic oxygen : $$\ce{ClO- -&gt; Cl- + O}$$
In reality, it would be combination of both in various ratio, depending on relative reaction rates,  all ending as mixture of sodium hydroxide, carbonate, chloride and chlorate.