If all bacteria in human gut are dead, can they be there again?
So the question your essentially asking is "Do certain types of bacteria like a specific nutrient, and if so will they dissipate or die off if I do not acquire that nutrient?"

Let's give a specific example for comparison. Lactose intolerance is a prevalent disorder among many people and those who do have the intolerance, if aware, tend to steer clear from lactose containing foods. Some studies have been shown that correlate lactose consumption to amount of lactose-containing bacteria in the gut. 

So I would say if your asking if you remove a nutrient from your diet will a particular bacteria suffer i.e die then yes. Although be aware that many bacteria are able to break down a variety of different nutrients, and in the case of a cupcake which is loaded with sugars, and fats, I would say a large majority of gut residing bacteria are able to use that as energy in one form or another.

Here's an article comparing lactose-tolerant, and lactose intolerant individuals, not chocolate, but a good start. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2898492/