or 100% of the 50% that are destroyed are the gut bacteria in the humans etc that got snapped

Fewer than 50% of the cells in "your body" contain your own DNA.

There are many more bacteria, since they are much much smaller than "your own" eukaryotic cells.

Where you end and your "gut flora" begin and end is not as clear as you might first believe.

50% fewer people working all critical sewer infrastructure, too