When somebody tells me their bees absconded this time of year the first thing I think of is Parasitic Mite Syndrome. I've only seen it a few times but usually there's a queen and a few bees left looking like they absconded when really they died off and the rest drifted, it can happen fast. I would check for lots of dead mites on the bottom board, mite feces (guanine, looks like white deposits in the cells). Or if there is a few pupae left, check them for mites. Also look for dead bees with crinkled wings or short abdomens on the bottom board or on the ground around the hive stand. If other colonies are close by do a mite count on them asap and you may have your answer as to why the hive is in that condition.