This is the kind of tiring hypothetical omnivores throw at vegans just to troll us, but I find it is usually better to answer them seriously, so:

###Why it's probably better not to eat the pig

If I do not eat the pig, it may be eaten by other humans who would normally buy farmed meat, thus reducing demand for such meat.

If not, it may be eaten by other animals (carnivores) whose interests I consider important as a vegan (animal ally?).

If that's not the case, it may be decomposed by micro-organisms which return nutrients to the soil.

This is the kind of tiring hypothetical omnivores throw at vegans just to troll us, but I find it is usually better to answer them seriously, so:

Why it's probably better not to eat the pig

If I do not eat the pig, it may be eaten by other humans who would normally buy farmed meat, thus reducing demand for such meat.

If not, it may be eaten by other animals (carnivores) whose interests I consider important as a vegan (animal ally?).

If that's not the case, it may be decomposed by micro-organisms which return nutrients to the soil.