There are many reasons why sage plants may die. The most important are not providing enough sunlight, or overwatering, which causes the roots to rot and the plant to wilt. Be sure not to over water it by checking for dryness before watering again. Another reason that can cause a sage plant to die is pests such as spider mites or aphids. These critters suck sap from the leaves of plants and will often kill them if left untreated.