Well, they are free to continue to use the name without trademark protection. Of course they then cannot prevent anyone else from using the name for whatever products and services the trademark granted protection for. So, arguably, they may be forced indirectly to choose a new name out of commercial considerations. Note that IP rights such as patents and trademarks do not grant a right for use by the owner but the right to stop third parties from using that what is protected.
So the court, to stop offending Native Americans with the name, are going to open the name up to be used by everyone. Liberal logic.