This would be a good question for your rheumatologist and your surgeon. Get both opinions and suggestions. Have you tried the new disease modifying antirheumatic drugs (DMARDs)? Usually a six-month trial of DMARDs and antiinflammatory drugs is tried before surgery.
Other conservative measures that help some patients include splinting and exercise. An occupational or physical therapist can supervise you in trying a home program. They can help you find ways to do painful or difficult tasks more easily. Special devices can be purchased to help you open doors, jars, or other assist with other similar activities.
A wrist fusion usually does work well to control pain. But as you noted it will limit your motion and reduce your function. For many RA patients the pain relief is worth the trade off.
Other treatment options include a partial fusion or even a joint replacement. Partial wrist fusion gives stability to the joint while saving some motion. And yes! Wrist joint replacement is possible now. It has the benefit of preserving motion. Wrist implants have improved over the last few years with better long-term results.