stick a bunch of nodes in your scene (just empty unity objects) name them node1,2,3,4,5 make your loop / path and number them in order.
Make an pathManager script that has a public transform[] nodeLoop; array and drag your nodes onto the array in order. Now you have a list of node/postions.
Now jsut hook it up to your existing OnTargetReached() make a function that just gets the next node position...
something like this
void OnTargetReached ()
{
new_targetPosition = pathManager.m.getNextPathPoint()
}
pathmanager has something like this...
int pathPoint=0;
Vector3 getNextPathPoint()
{
pathPoint++;
if(pathPoint >= nodeLoop.length)
pathPoint=0;
return nodeLoop[pathPoint];
}
sorry for the hasty pseudocode, but you should get the idea