Seeing how Akainu tanked a Quake and got up, one Roar isn't going to kill him. Or two for that matter. But if Acnologia keeps spamming then yeah it's over lol.
An impressive feat though it was, Acnologia did blow an entire island out of existence with pure ease.
I don't think he could tank even one attack.
to be fair, that attack was calced at city level + because the island was quite small, even under it as well.