Not many leagues or clubs have the financial means to sign a big-name player from the Premier League anyway. And players seldom move from the lower English leagues overseas either.
Whether the deadline is before the season or at end of August, the selling club could always choose not to sell if they can't get a replacement in. 35m for Carroll, new or old transfer deadline, we would still sell. At least with the new deadline, Liverpool and Southampton could settle the Coutinho and Van Dijk situations, move on and focus on their first match.