This is purely anecdotal evidence: I've been using hibernate on my latest, short campaign as the Scipii, and I have had about 3 messages so far about defeat being imminent - twice because Gaul was about to win, and once because of Egypt winning. In other short campaigns (I've played Brutii and Egypt) I've never had any such messages. This suggests to me that using hibernation to avoid reloads has resulted in a more expansive and aggressive AI.