Natural carbonation/bottle conditioning is a natural process. When your brew is in the fermenter the off gassing escapes through the airlock. When you add more sugar (at bottling time) the yeast is still active and will eat the sugar. With the cap on the bottle the gas has nowhere to go except back into the liquid/beer. This produces the carbonation bubbles and collects on the surface of the brew which we call "the head".
As for adding fruit and other components into the brewing process I ALWAYS recommend FIRST that you have a good drinkable beer BEFORE screwing with it.
If you add those to the brew and the brew sucks then you haven't wasted any ingredients.
Unless the beer is absolutely undrinkable and nasty beyond belief, you'll be hard pressed to find a homebrewer that will dump a batch. My worst batch ever involved the use of way too much molasses, which overpowered every other flavor and turned the bottles into timebombs. When I poured the beer into a glass, it would be all foam, and the bottle would foam over as well, and it has just a horrid flavor. And I STILL haven't dumped the entire batch, after almost two years. I occasionally try one, hoping beyond hope.
The only other time I've dumped a batch were when I broke a thermometer into the boil. Pure safety issue then.