Well yes, he can powerdown now, but it will be 13 weeks before he can sell all of that powered down stake (it is converted in 13 weekly intervals), and by the sound of it (assuming it happens) the new chain would be active before that.

Ps. please read this post i just made: https://steempeak.com/publish?edit=atma.love%2Freclaiming-our-sovereignty-during-these-chaotic-times
And i dont think he would re-buy more Steem. It seems he just wants his money back. Who knows what will happen .....

I know nothing! :-)