Plenty of people, sure. But I doubt that number would have come close to matching the number of copies the Xbox One version sold.
No way of knowing any specific amount, either way.
Still bad for SqEnix. If they wouldn't have some kind of partnership or marketing deal with Sony, they will get nothing from PS4s sold to XBO owners which will buy it just to play FFXV. But some sales from this 600k on XBO they would have lost. So, less money for them.
Like everyone else here, I can't say what would have been bad for Square Enix.