I assume you mean that day's entry is missing, not the entire list. If you come back after the battle's over, you should at least get the guild end ratings (assuming the latest versions).
I have a mountain of notes about various ways that the game client has failed to report data in the past. I haven't played in over a year, so I wouldn't have seen such a case recently, or any potential bug in the add-on either. The game API and add-on code haven't changed in quite a while.
(edit)
Oh! Are you referring to the player details, rather than the guild entries? In that case, yes, if the crash happens while leaving the battlefield, it's gone. Nothing can be done there.
Yes, player details. Merit counts, kill count, ranking in defense, heals, etc. All that was blank.
I was extremely mad because that war I broke my previous record of 338 kills and I desperately wanted it screenshotted and it turned out none of my guild mates had a copy of it then or now.