Even though it feels wrong that they lost their trademark, the Redskins have no choice but to accept the decision. The rights of the people are decided by the people and the officials they elect to office. Some may cry that it voilates their first ammendment rights, but remember, those rights are enforced by the will of the people.
From how I understand it they are still allowed to call themselves the Redskins, they just don't have the name and logo trademarked and may not be able to profit from it. This is in no way a first amendment violation, the amendment doesn't say that you have the right to trademark names, it just says you have the right to say what you want, a right that they clearly still have.
No, the revocation of the Redskins trademark does not violate the First Amendment because they are still free to use the term in question, they just are not allowed to exclusively profit from it or sue anyone for using it. U.S. Trademark law does not allow for the protection of terms which disparage a group of people, so the revocation was perfectly legal.
While the right to free speech is important in any democracy, hiding behind it as an excuse to continue a trademark that is offensive to a minority is completely against the spirit of it. There are too many cases where people abuse the first amendment to get their own way, and I'm glad an example has been set that this cannot always be how it works.