Chris Feaster sees Main Line Health clinicians for mammograms, breast MRIs, and other preventive screenings required due to her high risk of breast cancer. The 61-year-old Montgomery County resident has been panicked in recent weeks after Main Line sent patients a letter warning that the nonprofit health system’s contract with her insurer, UnitedHealthcare, may end later this month. Main Line is a leading provider of care across Philadelphia’s western suburbs, where it has four hospitals.