If you have not yet entered menopause, you still will be able to conceive if you stop taking the birth control pill.
As long as you are still having menstrual cycles, you potentially can conceive a child, even at 40 or 50. Oral contraceptives at 40 can help prevent pregnancy, but if you stop, you can still get pregnant. If you do not want any more children, you can look at an IUD such as mirena, which lasts about 5 years, or Essure coils in the fallopian tubes, which are permanent birth control and can be placed in the doctors office. You could also look at a uterine ablation which cauterizes (burns) the inside of the uterus so you no longer have periods and don't get pregnant. You have options to prevent pregnancy if you don't want to take birth control pills.