onBeforeSplit

fires before merged cells are split

boolean onBeforeSplit(number row,number column,array value, [string page] );

row

numberthe number of the row that the span starts with column

numberthe number of the column that the span starts with value

arraythe array with values of the deleted span pagestringthe name of the sheet

boolean

returning false will prevent splitting of merged cells

$$("ssheet").attachEvent("onBeforeSplit", function(row, column, value, page){
    // some code here
    return true;
});

Details

return false to block cells' splitting