True, the PR concerns are valid for the NFL. I think they are somewhat disingenuous, the league is still built on violence that wrecks people's bodies and brains and that won't change if Tua has to retire. But if he had another hit that had catastrophic sequela it would certainly be a bad look. How many concussions is too many? There is no guideline on that, it would be arbitrary.
Probably the simplest thing for the league and Dolphins would be if Dolphins medical staff just refused to clear him ever again.
But I'm not sure what other enforcement mechanism the NFL could take if Tua still wants to play. I don't think the league has any way of making that happen apart from somehow leaning on the nominally independent medical staff of any NFL team that wanted to sign him.
Probably the simplest thing for the league and Dolphins would be if Dolphins medical staff just refused to clear him ever again.
But I'm not sure what other enforcement mechanism the NFL could take if Tua still wants to play. I don't think the league has any way of making that happen apart from somehow leaning on the nominally independent medical staff of any NFL team that wanted to sign him.