Last month’s defeat of a three-and-a-half-million dollar referendum could mean more than 20 percent of the teachers in the Delavan-Darien School District will lose their jobs. Some voters are surprised at the effect their “no” vote had — not realizing that nearly 40 teaching positions could be eliminated. The measure failed by about 500 votes. Starting next fall, about 275 fourth- and fifth-graders at Darien Elementary will be transferred to other school buildings in the district. Officials plan to put the referendum in front of voters again this fall, hoping for a different outcome.