Great question.  Your idea here might be worth trying, but do not do it without first discussing this with your doctor.  It sometimes takes time, and trial and error, to find the right concoction of meds to control your asthma.  Ideally you'll want the best asthma control with the least amount of medicine, and if Singulair alone works great.  If it doesn't, then your doctor might recommend putting you back on Symbicort or some other medicine.    You and your doctor are a team and you need to work together to keep your asthma under good control.  You'll also want to keep up to date on all the new asthma meds and asthma wisdom, as you never know when something new might become available to help you.  A great place to do that is right here.   A great article worth reading is: Which asthma med works best?