Some have said that would violate the settlement agreement between UND and the NCAA. That's not true at all. I reached out to the UND leadership to get clarification. Here's the response that I received.
Eric, thanks for the email and the support for our university. The NCAA says there would not be a violation of the settlement agreement as far as they are concerned if UND didn't adopt a new nickname. However, the NCAA did say that if fans resumed using Sioux or Fighting Sioux, the NCAA believes other schools will complain and that, in turn, would very likely result in sanctions. The NCAA does seem to believe that UND has done its best to comply with the settlement agreement.
Executive Associate Vice President for University Relations