What is the prognosis for Polymyositis?

So I needed to get real and face what might be going to happen if the immunosuppressants do not work to stop the progression of the disease. Here is what I found:
The prognosis for polymyositis varies. Most people respond fairly well to therapy, but some have a more severe disease that does not respond adequately to therapies and are left with significant disability. In rare cases individuals with severe and progressive muscle weakness will develop respiratory failure or pneumonia. Difficulty swallowing may cause weight loss and malnutrition. National Institute of Neurological Disorders and Stroke

The progression of PM and DM varies considerably from person to person. Immunosuppressants can improve strength, although not all patients respond, and relapses may occur. PM and DM can lead to increasing weakness and disability, although the life span usually is not significantly affected. About half of the patients recover and can discontinue treatment within five years of the onset of their symptoms. About 20% still have active disease requiring ongoing treatment after five years, and about 30% have inactive disease but some remaining muscle weakness. Gale Encyclopedia of Medicine

Although polymyositis and dermatomyositis are regarded as treatable disorders, prognosis is not well known, as in the literature long‐term outcome and prognostic factors vary widely.  U.S. National Library of Medicine