This use of Sutent or Nexavar, to prevent recurrence when all cancer has been removed surgically, is called adjuvant treatment.
Before Sutent and Nexavar, there was no approved adjuvant treatment for RCC, but some studies were done with interferon, low dose interleukin-2 (wich both have significant side effects), and vaccines mades from the patients own tumor. Sutent and Nexavar are both newly approved; it will take years before we know if they really work as an adjuvant treatment.
Studies to see if specific adjuvant treatments work take a long time to complete, and quite a few patients to show results because some patients will never have a recurrence. I have a relative who has gone 12 years without a recurrence (stage 1), It is uncommon, but certainly not unknown for the RCC to recurr after an even longer period. Also, with RCC, since the cancer sometimes comes back many years after surgery, a study done which follows patients, say two years, will miss many instances of patients having recurrences later than this. (See http://cancerguide.org/adjuvant.html for more detailed information about adjuvant treatment). Most recurrences do occur within a few years of surgical treatment. When a recurrence occurs many years after surgical treatment, it is more likely to come back in only one or two places, and can often be treated with surgery--or another drug might have been developed in the meantime--if the recurrence is discovered quickly. This is why RCC patients should have follow-up studies done for the rest of their lives. See http://cancerguide.org/index.html for good information on researching options and deciding which treatment to pursue.
At this point, good data from studies of Stuent and Nexavar as adjuvant treatments really don't exist, so we don't really know if either of these drugs will prevent recurrences. However, there is no other approved adjuvant treatment. Your wife will have to decide whether the downside of the side effects are worth the possible (but as yet unknown) benefit. It is a difficult decision.
Also, there is an email support list specific to RCC/Kidney cancer. See http://cancerguide.org/kofaq/ to join.