I actually found this info a few months ago, and it might have even been an old thread on here...
From memory, it said that beer continues to hydrate you somewhat until you reach a certain ABV that was in the 7.?? range, where it loses all it's hydration value...but it didn't mention anything about it depending on how much water your body needs, but that's fairly obvious I suppose...
So, I wonder if you drank 5% beer all day everyday instead of water, if you'd stay hydrated enough to survive, but still not quite at the level you should be...
From experience, I drink mostly stouts, IPAs and other strong ales, and after consuming 8-10 in the course of a night, I feel the need to drink water throughout, and definitely at the end of the night...