How long does a Wheeler Mock Orange shrub live?

We planted 6 Dwarf Mock Orange shrubs in a raised planter next to our home about 10 years ago. They remained small and did well for years. One has died and others have yellowed leaves. We use Miracle Grow fertilizer. Mulch has been applied. Do these Dwarf shrubs have a short life span? We have several larger Mock Orange bushes and they have been doing well for years. Should I pull up the dying plants and replant? We live in El Paso, Texas. Rainfall is about 8 inches per year.