It depends on the bacteria, when in it’s lifecycle half of it is killed, and what half is killed. To keep things short, the odds are in the bacteria’s favor. Suppose if half the bacteria in your gut died right now how long do you think it would take for the bacteria population in your gut to return to pre-snap levels? A month? A year? Decades? How about less than an hour. Bacteria reproduce exponentially and on average, a bacterial generation lasts 20 minutes. Meaning that every 20 minutes the population doubles, assuming there are no deaths in the population during this time. If there is space for bacteria to grow, they will.
Just a bit of history, in WWII the Allies didn’t know for certain that the Holocaust had occurred. Remember that it was the 1940s, information could travel quickly but only so much. It wasn’t as easy for them back then to pickup the metaphorical ‘signal’ of the Holocaust happening to the ‘noise’ the rest of the war was making. So while there were rumors of mass executions of Jewish people as early as the summer of 1941, it’s often said that the Allies didn’t know about the Holocaust until winter 1945. Now when the Allies went from ignorant, to suspicious, to all but certain but with doubts and finally to certain without a doubt has been debated for decades and will probably be debated until the sun expands and swallows the earth whole. There was definitely a lot of hateful rhetoric being spouted about Jewish people in the 1930s that maybe should have been stopped before it nearly took over Europe, but looking back at history we have the advantage of hindsight.