Everyone gets replaced. Someone always steps in. But for the better? That usually doesn't happen when its your best player, not unless you replace him with a better player, and I don't see that happening this year. Now, maybe improvements happen elsewhere and those improvements, plus whatever you can do to minimize the dropoff between your departed best player and his replacement, can leave you with a better team. But it won't be better than if your best player had simply stayed with you.
So, will that happen this year, will advancements elsewhere be so significant as to improve the team? Maybe. But claims of "off season" improvements by [insert player name], better play because of better conditioning of [insert player name], and upgrades from the soon-to-be eligible [insert sit-out transfer or freshman] is yearly fare around here. The power of off season improvements on this board is so great that it bulldozes through anything, even the transfer of your best, most experienced player, and grows in strength through words on messages boards until it becomes a well-polished, undeniable truth that can't be countered.
Then the games start. Maybe we'll be better this year. But it won't be easy, and it is far from certain or even the most likely outcome.