Can people stay on advair indefinitely or does something bad happen?

Consider alternative. One round of oral steroids is worth a couple of years of daily inhaled steroids, plus it provides better symptom control. There may be some risk to the bones and eyes at the highest doses, but it is safe in general and safer than the alternative- risking bad asthma exacerbations. If your asthma requires advair, i'd recommend a visit to an allergist to see what's keeping your asthma active.