To sum it up: RA means your immune system attacks healthy joints, which leads to inflammation that can cause pain, stiffness, swelling, weakness and permanent damage or disability to bones and joints. There is no known cause or cure. RA must be primarily self-managed through medication, lifestyle changes and frequent monitoring by a rheumatologist.
Rheumatoid Arthritis is also a systemic disease, which means inflammation that afflicts primarily the joints can also cause problems in the rest of the body. These problems are called comorbidities - medical conditions present simultaneously with (and either caused or affected by) RA. You can read more about arthritis comorbidities here.
RA is also a progressive disease, meaning it will most likely continue joint destruction throughout your lifetime. Disease progression usually presents itself through a continual series of flares (periods of painful disease activity) and remissions (periods of little or no pain or measurable disease activity). It can also mean that RA could remain in a few joints or affect all joints in the body.
I think it is important to note that RA itself is not fatal, but it is a serious disease. Complications from rheumatoid arthritis (see comorbidities above) can lead to life-threatening situations, but proper management and care from appropriate doctors can help avoid or lessen the severity of such complications. It is of utmost importance to take prescribed medications, adjust your lifestyle, avoid stress and see your doctors to monitor your health when living with RA.