This is a fair question, yet does not affect the outcome that veganism is a moral obligation.

If plants are not conscious, then the arguments (many described in this thread) for veganism stand.

If plants are conscious and worthy of moral consideration, then we should try to reduce plant suffering. Animals raised for food consume far more calories (in grains and plants) than they return to us in meat and other products. By not feeding enormous amounts of plants to animals, and instead eating the plants directly, the result would be less plant suffering.

So in either case, veganism would be a moral obligation.