Dorsey’s Square had all the Google juice around the word, so it wasn’t likely causing any lost sales. But for credibility, there is no choice but to own the basic .com version of your brand. (Plus, they would hate to get confused with the board game of the same name.)
It may not yet be a done deal. I don’t see any confirmation of a sale on the Web. Square.com is currently being redirected, very slowly right now, to squareup.com. And the Whois record still shows that square.com is owned by Square Enix Holdings Co. Ltd. in Tokyo, the makers of the popular video game, Final Fantasy.