Before a new connection is established check whether the source already has outgoing connections, If so remove it. Assuming that exit elements have exit
class:
jsPlumb.bind('beforeDrop', function(ci){ // Before new connection is created
var src=ci.sourceId;
var con=jsPlumb.getConnections({source:src}); // Get all source el. connection(s) except the new connection which is being established
if(con.length!=0 && $('#'+src).hasClass('exit')){
for(var i=0;i<con.length;i++){
jsPlumb.detach(con[i]);
}
}
return true; // true for establishing new connection
});