The "opt in" was him keeping his Twitch contract. Now others might profit off his success - and he's still rich. Seems like a win-win to everyone.
Not surprised if he just deletes his Twitch channel and makes big public thing about it so Twitch can't go and try take it over for further use. This is Twitch trying to hijack his brand and reach which is quite big breach of trust. Thing would be totally different had Twitch coordinated these promotion efforts with Ninja instead of repurposing his channel without questions asked.