I don't think this is the problem people are experiencing, I think OPs issue was that his macbook isn't meant to be sleeping, just have the display off, yet wifi seems to be cutting off when this happens.
I recently noticed this when trying to upload my photo collection to iCloud Photo Library, started it before i went to bed, went back in the morning to find it hadn't made any progress. I got around it by ticking "Prevent computer from sleeping automatically when display is off". The option is only available for the power adapter energy settings however, not for on battery.