I grew up in GF area, played for the Sioux and was a militant 'keep the nickname' guy until it just wasn't worth what it was going to cost. I also have a house full of Sioux stuff that will last me as long as I am on this earth.
They fought it to tune of millions of dollars but it became untenable by the end. The pain that was going to be imposed went way beyond any potential gain by keeping the nickname. I believe we got jobbed on playoff seeding or left out completely as punishment in multiple sports.
If we'd have chosen a better nickname like Nodaks, I think the transition wouldn't be such a big deal.