What is the estimated life span of someone with copd, empysema who only have 30% of lung function?

Difficult to assess: I do not know exactly what you mean by 30% lung function. Are you referring to pulmonary function test values. Assuming lung function is 30% it sounds ominous, life expectancy could be less than five years. Having said that, i suggest to see a pulmonologist to assess taking into consideration all factors.

Varies...: The most important treatments include smoking cessation and oxygen therapy, if the person's oxygen level is low enough to warrant it. Bronchodilator and steroid inhalers are also typically used in treatment. The disease is slowly progressive and smoking cessation and oxygen therapy do tend to slow progression. The rate of progression varies widely between patients so difficult to predict.

Rate of decline: Unfortunately a patient with emphasema with 30% function (as represented by the fev1) will feel pretty limited - life expectancy is better guaged by how quickly that lung function is disappearing - someone who quit smoking 20 years ago and is now only losing the normal amount may survive for years - but someone who is still smoking or is rapidly getting worse may sucumb much faster.